September, 1960 P H Y S I O T H E R A P Y Page 3 POST REGISTRATION COURSE CHEST CO U RSE A P o s t R e g is tra tio n C o u r s e o n “ C h e s ts ” o r g a n is e d b y th e N o r t h e r n T r a n s v a a l B r a n c h o f th e S o u th A fric a n S o c ie ty o f P h y s io th e r a p y w a s h e ld in th e P h y s io th e r a p y S c h o o l. P re to ria H o s p ita l, o n F r i d a y a n d S a tu r d a y , M a y 2 7 th a n d 2 8 th . S ix ty -o n e m e m b e r s a n d tw e n ty -six s tu d e n t m e m b e rs o f th e S o i.th A f ric a n S o c ie ty o f P h y s io th e r a p y a tte n d e d th e c o u rs e , m a n y c o m in g f r o m a s f a r a s C a p e T o w n , K im b e r le y , E a s t L o n d o n , D u r b a n , P ie te r m a r itz b u r g , B lo e m fo n te in , B a rb e r to n a n d m a n y m o r e to w n s in t h e T r a n s v a a l. T h e c o u rs e w a s o p e n e d b y D r . P . N . S w a n e p o e l, S u p e r ­ in te n d e n t o f th e P re to ria G e n e r a l H o s p ita l, w h o w e lc o m e d th e v is ito rs, s p o k e o f t h e im p o r t a n t p a r t p la y e d b y th e P h y s io th e r a p is t in a ll C h e s t w o r k a n d p a r tic u la r ly th e n e c e ssity o f th e m b e in g a m e m b e r o f a n y S u rg ic a l C h e s t U n it. O n th e first d a y o f th e c o u r s e , le c tu re s w e re g iv en b y : — D r. L. M . J o n c k , S e n io r L e c tu re r in A n a t o m y , P re to ria U n iv e rsity . D r . C . J. L a b u s c h a g n e , S e n io r L e c tu re r in P h y s io lo g y . P re to ria U n iv e rs ity . D r. L D . E ra s m u s , m e m b e r o f th e F a c u lty o f M e d ic in e , P re to ria U n iv e rs ity . D r. J. C . v. d. S p u y , S e n io r C h e s t S u rg e o n , P r e to r ia H o s p ita l, w h o a ls o s h o w e d a v e ry w o n d e r fu l film o n “ O p e n H e a r t S u rg e ry ” . T h e se c o n d d a y o f th e c o u r s e w a s g iv e n u p e n tir e ly to th e t r e a tm e n t o f C h e s t C o n d i t i o n s b y P h y s io th e r a p y . M iss M . W h ite , M .C .S .P ., L e c tu re r in th e D e p a r t m e n t o f P h y s io ­ th e r a p y , C a p e T o w n U n iv e rs ity , g a v e a ll t h e le c tu re s a n d d e m o n s tr a tio n s . M iss W h ite ’s le c tu r e s a n d d e m o n s tr a t i o n s w e re o f th e h ig h e st q u a lity — c le a r a n d d e fin ite , s h e c o v e re d a tr e m e n d o u s a m o u n t o f g r o u n d , d e v o tin g th e m o r n in g se ss io n to m e d ic a l a n d th e a f t e r n o o n to s u rg ic a l c o n d itio n s , a n d u sin g P h y s io ­ th e r a p y s tu d e n ts a n d re a l p a tie n ts to illu s tr a te h e r p o in ts . T h e . N o r t h e r n T r a n s v a a l B ra n c h w o u ld lik e to e x p re ss th e ir t h a n k s to M is s M . M c D o w e ll, M .C .S .P ., StafT o f th e P h y s io th e r a p y D e p a r t m e n t o f th e B r o m p to n C h e s t H o s p ita l, L o n d o n , E n g la n d , f o r v e ry k in d ly le n d in g h e r o w n film s w h ic h M iss W h ite u se d t o d e m o n s tr a t e t h e tr e a tm e n ts o f th e a s th m a tic , in d iv id u a lly a n d in g r o u p s . In a d d itio n t o th e le c tu r e s a n d d e m o n s tr a t i o n s tw o larg e r o o m s w e re se t a s id e . O n e a s p e c im e n r o o m , g a v e a n e x c e lle n t d is p la y o f X - ra y s o f C h e s t c o n d itio n s , p h o t o g r a p h s o f c a s e s d e m o n s tr a t i o n s in c is io n lin e s p o s itio n o f d r a in a g e t u b e s , ty p ic a l p o s tu r e s , e tc ., o f p o s t- o p e r a tiv e c h e s t c o n ­ d itio n s . A lso m a n y A n a to m ic a l a n d P a th o lo g ic a l sp e c im e n s o f lu n g s w ere d is p la y e d . I n th e se c o n d r o o m w e re o n v iew m o d e r n a n d u p - t o - d a t e a p p a r a t u s a n d a ls o a b o o k s h o p w ith the, la te s t p u b lic a tio n s a n d p a m p h le ts o n C h e s t C o n d itio n s a n d m a n y o th e r m e d ic a l b o o k s . I n th e ir f re e p e r io d s th e m e m b e r s h a d a n o p p o r t u n it y o f m e e tin g in th e s e r o o m s a n d d is c u s s in g n o t o n ly C h e st c o n d itio n s b u t a ls o o t h e r P h y s io th e r a p y m a tte r s . W e s h o u ld lik e to e x p r e s s o u r t h a n k s to a ll w h o c o - o p e r a te d so f u lly a n d h e lp e d t o m a k e t h e c o u r s e s u c h a su c c e ss ; to D r . S w a n e p o e l fo r h is s u p p o r t , to all t h e L e c tu re r s , to th e p a tie n ts a n d s tu d e n ts w h o a c te d a s m o d e ls f o r M iss White,., to th e S ta f f o f th e X - ra y D e p a r t m e n t f o r th e lo a n o f film s a n d v ie w in g b o x e s , to M r. M a ra is a n d th e S ta f f o f th e P h o t o g r a p h ic D e p a r t m e n t f o r th e in te r e s t a n d t r o u b le th e y to o k to g iv e u s s u c h e x c e lle n t p h o t o g r a p h s , t o th e d o c t o r s f o r th e lo a n o f sp e c im e n s, to t h e S c h o o l S taff, p a r t i c u l a r l y th e S e c r e ta r y , M rs. S m ith , f o r a ll th e “ b e h in d t h e sc e n e s w o r k ” w h ic h h e lp e d in th e s m o o t h r u n n in g o f t h e c o u r s e , a n d la s tly , t o th e s tu d e n ts w h o w o r k e d so h a rd a n d se rv e d all t h e m e a ls w ith efficien c y a n d c h a r m . A SP E C T S O F R E SP IR A T IO N B y D r . C . J . L A B U S C H A G N E , M .S c ., P h .D . S e n io r L e c tu re r , D e p a r t m e n t P h y sio lo g y , U n iv e r s ity o f P r e to r ia . A L e c tu re g iv e n to D e le g a te s a n d M e m b e r s o f th e S o u th A fr ic a n S o c ie ty o f P h y s io th e r a p y on th e f i r s t d a y o f th e “ C h e st C o u rse ” , w hich w a s h e ld a t th e P re to r ia H o s p ita l S c h o o l o f P h y sio th e r a p y , on M a y 2 1 th a n d 2 8 th , 1960. What causes an Inspiration? T h e im m e d ia te c a u s e o f a n in s p i r a t i o n is th e f a c t t h a t th e th o r a c ic c a v ity in c re a s e s in siz e in a ll d im e n s io n s . B e c a u se th e lu n g s a r e a tta c h e d t o th e t h o r a c ic w a lls a n d u p p e r su rfa c e o f th e d i a p h r a g m (v is c e ra l a n d p a r ie ta l p le u r a e ) th e y a re str e tc h e d o u t to t h e e x te n t t h a t th e th o r a c ic c a g e e n ­ larg es. (H e n c e t h e im p o r ta n c e o f n o r m a l e la s tic ity o f th e lu n g s.) S in c e th e p u l m o n a r y v o lu m e in c re a se s, th e i n t r a p u lm o n a r y p re s s u re d e c re a s e s (B o y le ’s L a w — p r e s s u re — in v e rse ly p r o ­ p o r tio n a l to v o lu m e ), a n d , t h e lu n g s b e in g c o n n e c te d w ith th e e x te r io r v ia t h e a i r p a s s a g e s , a ir flo w s p a s siv e ly in to th e m u n til in tra p u l m o n a r y p r e s s u re = a t m o s p h e r ic p re s s u re . T h e e x te n t o r vo lu m e o f t h e i n s p ir a tio n is th e r e fo r e d e p e n d a n t o n ; (i) th e e x te n t o f in c re a s e in t h e size o f th e th o r a c ic c a v ity , a n d (ii) e la s tic ity o f t h e lu n g s. W ith n o r m a l, q u ie t (e u p n e ic ) b r e a t h i n g th is v o lu m e a m o u n ts to 5 0 0 m l.— so -c a lle d tid a l a ir. A b n o r m a l c o n ­ d itio n s o f th e th o r a x , p le u r a e o r re d u c e d e la s tic ity o f th e lu n g s will th e r e fo r e affe c t th e tid a l v o lu m e . What causes enlargement o f the thoracic cage? T h is is th e r e s u lt o f th e sp e cific s t r u c t u r e o f its b o n y f ra m e w o r k a n d th e c o n tr a c tio n o f c e r ta in m u sc le s th e in sp ir a to r y m u sc le s. O f th e s e th e d ia p h r a g m a n d e x te r n a l in te r c o s ta ls a r e t h e m a in o n e s c o n c e r n e d in e u p h e ic b r e a th in g . T h e i r c o n t r a c t i o n e n la r g e s th e th o r a c ic c a g e in a ll d im e n s io n s . T h e c o n t r i b u ti o n o f e a c h o f th e s e tw o se ts v a rie s in d iffe re n t in d iv id u a ls a n d in th e tw o se x es. G e n e r a lly th e d i a p h r a g m a c c o u n ts f o r 6 0 % o f th e in s p ir e d a ir — d i a ­ p h r a g m a t i c b r e a th in g — a n d th e in te r c o s ta ls f o r th e r e m a in in g 4 0 % — c o s ta l b r e a th in g . W ith a f o rc e d i n s p ir a tio n a d d itio n a l m u sc le s c o m e in to p la y : (i) N E C K ^ s c a ' e n '^ s t e r n o c l e i d o m a s t o i d ; . (ii) S H O U L D E R ^ ce“ s . A d e e p i n s p ir a tio n is th e re s u lt o f c o n t r a c t i o n o f a l l th e in s p ir a to r y m u sc le s, r a t h e r t h a n o f a sp e cific o n e o r g r o u p . W h e n c e r ta in in s p i r a t o r y m u sc le s a r e p a r a ly z e d (e .g . d i a ­ p h r a g m ) o th e r s c o m e in to p la y a n d r e s p ir a tio n is m a in ta in e d in s o m e p a tie n ts c h ie f ly b y th e n e c k a n d s h o u l d e r m u sc le s R ep ro du ce d by S ab in et G at ew ay u nd er li ce nc e gr an te d by th e P ub lis he r (d at ed 2 01 3. ) a n d in o th e r s a lm o s t so le ly b y th e a b d o m in a l m u s c le s. It is in d e e d s u r p r is in g h o w few m u sc le s c a n m a in ta in a d e q u a t e v e n tila tio n o f th e lu n g s in e u p n e ic b re a th in g . T h e i n s p ir a to r y v o lu m e w ill th e r e fo r e f u r t h e r d e p e n d o n : (i) t h e d e g re e o f c o n tr a c tio n o f a specific m u sc le , a n d (ii) th e n u m b e r o f in s p ir a to r y m u sc le s c o n tr a c tin g . M a x im a l c o n tr a c tio n o f a ll i n s p ir a to r y m u sc le s c a u s e s m a x im a l in c r e a s e in t h e siz e o f t h e th o r a c ic c a v ity w ith r e s u lta n t m a x im a l in s p ir a to r y v o lu m e . T h is n o r m a lly c o n s is ts o f : (i) 5 0 0 m l. tid a l a ir, (ii) 2 ,5 0 0 m l. in sp ira to ry reserve a ir. Why do the inspiratory muscles contract? T h is h a p p e n s b e c a u s e nerve im p u lse s c o n d u c te d to th e m a lo n g th e r e s p i r a t o r y n e r v e s, a re tra n s fe r r e d t o t h e m u s c le fib re s . A n e rv e im p u ls e is a p h y s ic o -c h e m ic a l d i s t u r b a n c e p r o p a g a te d a t h ig h v e lo c ity a lo n g t h e n e rv e fib re a n d is o f ' t h e n a t u r e o f a n e le c tric c u r re n t. T h e d e g re e o f c o n tr a c tio n th e r e fo r e d e p e n d s o n : (i) t h e n u m b e r o f m u s c le fib r e s (in a m u s c le ) re c e iv in g im p u ls e s a n d h e n c e c o n tr a c tin g , a n d (ii) th e n u m b e r o f m u sc le s c o n tr a c tin g . T h e a b o v e tw o f a c to r s a r e c o n d itio n e d b y : (i) t h e to t a l n u m b e r o f im p u lse s r e a c h in g a m u s c le p e r u n it o f tim e , a n d (ii) t h e fre q u e n c y o f th e im p u lse s . N e r v e im p u ls e s a r e d is c h a rg e d b y n e rv e cells o r neurons. W ith e u p n e ic b r e a th in g t h e d is c h a rg e o f im p u lse s b y re s­ p i r a t o r y n e u r o n s is a s y n c h ro n o u s , i.e ., s o m e n e u r o n s d is c h a rg e a c tiv e ly w h ilst o th e r s a r e q u ie s c e n t. O b v io u s ly th e n , t h e g r e a te r th e n u m b e r o f d is c h a rg in g n e u r o n s , th e • g r e a te r t h e n u m b e r o f c o n tr a c tin g m u s c le fib re s a n d m u sc le s. N e r v e im p u lse s a r e a lw a y s d is c h a rg e d in tr a in s o r v o lley s. W ith in a v o lley im p u lse s fo llo w e a c h o t h e r a t a specific fre q u e n c y , w h ic h m a y v a ry b e tw e e n 5— 1 0 0 /se c . T h e h ig h e r t h e fre q u e n c y , th e m o re p o w e rfu l th e e n s u in g c o n ­ tr a c tio n . W ith e u p n e ic b r e a th in g o n ly p o r t io n o f th e a v a ila b le n e u r o n s d is c h a rg e a t re la tiv e ly lo w fre q u e n c y . W ith a m a x im a l i n s p ir a to r y e ffo rt, a ll a v a ila b le n e u r o n s d is c h a rg e a t m a x im u m fre q u e n c y . Where do the impulses come from? T h e im m e d ia te s o u r c e o f t h e im p u ls e s a r e t h e m o to r n eu ro n s in th e a n te r io r h o r n s o f th e s p in a l c o r d se g m e n ts C 3 , 4 a n d 5 a n d T 2 — 6 . Im p u ls e s r e a c h in g th e s e n e u r o n s a r e re la y e d b y th e m to th e d ia p h r a g m a lo n g t h e p h r e n ic n e rv e (C 3 , 4 a n d 5) a n d to th e in te r c o s ta l m u s c le s a lo n g th e i n te r c o s ta l n e rv e s (T 2 — 6 ). H o w e v e r , th e se m o t o r n e u r o n s sim p ly re la y im p u ls e s — th e y d o n o t g e n e ra te im p u lse s. G e n e r a tio n o f r e s p ir a to r y im p u ls e s is a f u n c tio n o f n e u r o n s s itu a te d h ig h e r u p in th e b r a in ste m , viz. th e m e d u lla o b l o n g a t a a n d p o n s . T h e s e n e u r o n s p o sse s s th e a b ility o f c o n tin u o u s a u t o m a t i c , re p e titiv e im p u lse g e n e r a tio n , th e r e s u ltin g im p u lse s b e in g c o n d u c te d f r o m th e b r a in ste m to t h e m o t o r n e u r o n s c o n c e r n e d in th e s p in a l c o rd a lo n g th e r e tic u lo s p in a l tr a c t. T h e n u m b e r o f r e s p ir a to ry n e u r o n s d is c h a rg in g im p u ls e s a n d t h e fre q u e n c y o f th e ir d is c h a rg e th e r e f o r e u ltim a te ly d e te r m in e th e d e g re e o f in s p ir a tio n . T h e s e f a c to r s a r e in t u r n , d e te r m in e d b y th e su m to ta l o f all in flu e n c e s im p in g in g u p o n th e r e s p ir a to ry n e u r o n s . S u c h in flu e n c e s m a y b e o f tw o fo ld n a tu r e : (i) c h e m ic a l; (ii) n e rv o u s . Chemical. T h e slig h te s t c h e m ic a l c h a n g e in th e e n v ir o n m e n t o f th e r e s p ir a to r y n e u r o n s ( b lo o d in te r s titia l flu id , in tr a c e llu la r flu id ) a lte r s th e ir p a t t e r n o f im p u lse g e n e r a tio n a n d d is ­ c h a rg e . I n c re a s e d p C 0 2 o r a c id ity a c tiv a te s m o r e r e s p ir a to r y n e u r o n s a n d in c re a se s th e f re q u e n c y o f th e ir d is c h a rg e w ith r e s u ltin g d e e p e r in s p ir a tio n . C o n v e rs e ly d e c r e a d e d — p C 0 2 o r in c re a s e d a lk a lin ity le a d s t o a s h a llo w i n s p ir a tio n o r a p n o e a — ( te m p o ra r y c e s s a tio n o f b r e a th in g ) . I n th is l a t t e r i n s ta n c e th e re s p ir a to ry n e u r o n s d is c h a rg e n o im p u ls e s — th e y a r e inhibited. Page 4 September, 1960 Nervous. T h e r e s p ir a to r y n e u r o n s a r e c o n s ta n tly b o m b a r d e d b y n e rv e im p u ls e s o r ig in a tin g e ls e w h e re w ith in t h e c e n tr a l n e r v o u s sy s te m o r p e r ip h e r a l o r g a n s . A d e e p i n s p ir a tio n c a n be m a d e v o lu n ta r ily o r th e b r e a th c a n b e h e ld , i.e. n o in s p ir a tio n m a d e a t a ll. S u c h e x c ita to r y o r i n h ib ito r y im p u ls e s b o m b a r d th e r e s p i r a t o r y n e u r o n s f r o m t h e c e r e b r a l c o r te x a n d a r e c o n d u c te d t o t h e b r a in s te m a lo n g t h e e x tr a — p y r a m id a l sy ste m . T h e s o b b in g in s p ir a tio n o f g r ie f is th e r e s u lt o f im p u ls e s o r ig in a tin g in t h e c e r e b r a l c o r te x a n d h y p o th o la m u s . S im ila rly , t h e c h a n g e d i n s p ir a to r y p a t t e r n in o th e r a c tiv itie s , e.g. ta lk in g , s in g in g , sn e e z in g , c o u g h in g , s ig h in g , e tc ., is t h e r e s u lt o f n e r v o u s b o m b a r d m e n t o f th e r e s p ir a to r y n e u r o n s f r o m t h e n e r v e c e n tr e s c o n c e r n e d . S te p p in g u n d e r a c o ld sh o w e r c a u s e s a s u d d e n d e e p in s p ir ­ a t i o n — g a s p — d u e to p e r ip h e ra l im p u ls e s f r o m th e sk in r e a c h in g th e r e s p ir a to r y n e u r o n s a n d g r e a tly in c re a s in g th e i r a c tiv ity . What is the respiratory centre? T h is is th e n a m e g iv e n to a ll th o se n e u ro n s c o n c e r n e d w ith t h e in itia tio n a n d m a i n te n a n c e o f r e s p ir a tio n a n d lo c a te d , w ith in t h e lo w e r p a r t o f t h e b r a in s te m , i.e. p o n s a n d m ed u llaJ! T h e y a r e s p r e a d d iffu s e ly t h r o u g h o u t t h e m e d u lla a n d lo w e r p a r t o f th e p o n s a n d it is d o u b t f u l w h e th e r th e y f o rm a n a n a t o m i c u n it. H o w e v e r , th e ir m a in f u n c tio n is n o t o n ly to p r o d u c e a n in sp ir a tio n , b u t to m a in ta in r h y th m ic b r e a t h i n g i.e., i n s p i r a t i o n — e x p i r a t i o n ; i n s p i r a t i o n — e x p i­ r a t i o n , etc. T h e r e s p i r a t o r y c e n tr e is th e r e f o r e s u b d iv id e d in t o : (i) in s p i r a t o r y ( a p n e u s tic ) c e n tre , (ii) e x p i r a t o r y c e n tr e , (iii) p n e u m o ta x ic c e n tre . A g a in th e s e a r e m o r e o f p h y s io lo g ic a l t h a n a n a to m ic a l u n its . T h e i n s p ir a to r y c e n tr e ( in s p ir a to r y n e u r o n s ) is re s p o n s ib le f o r m a in ta in e d i n s p ir a tio n (a p n e u s is ) — a s d e s c rib e d . T h e e x p ir a to r y a n d p n e u m o ta x ic c e n tr e s , t o g e t h e r w ith th e so -c a lle d v a g a l m e c h a n is m , a r e r e s p o n s ib le f o r e x p i r a t i o n — t o b e d e s c rib e d n o w . What causes an expiration? T h e t h o r a c ic c a v ity d e c re a s e s in siz e ; th e e la s tic lu n g s re c o il a n d d e c r e a s e in v o lu m e ; t h e i n t r a p u lm o n a r y p r e s s u re is ra ise d t o a b o v e a t m o s p h e r ic p re s s u re a n d a i r flo w s o u t a l o n g t h e r e s p ir a to r y p a s sa g e s . T h is d e c re a s e in t h e size o f th e th o r a c ic c a g e is d u e to re la x a tio n o f t h e in s p ir a to r y m u sc le s (in e u p n e ic b r e a th in g ). T h e e x p ir a to r y v o lu m e is t h e r e f o r e = i n s p ir a to r y v o lu m e = tid a l a i r = 5 0 0 m l. H o w e v e r, w ith a f o r c e d e x p ir a tio n , a c tiv e c o n t r a c t i o n o f ' th e e x p ir a to r y m u s c le s o c c u r s : (i) in te r n a l in te r c o s ta ls , (ii) a b d o m in a l m u sc le s. T h e s e m u s c le s re c e iv e th e ir im p u ls e s f r o m t h e e x p ir a to r y c e n tr e a lo n g t h e s a m e r o u te a s t h a t d e s c rib e d f o r t h e in ­ s p i r a t o r y im p u ls e s . W ith m a x im a l c o n tr a c tio n o f th e e x p i r a t o r y m u sc le s, i.e. m a x im a l d e c r e a s e in t h e size o f t h e c h e s t c a v ity , th e e x p i r a t o r y v o lu m e a m o u n t s to 1,500 m l. T h is c o n s is ts o f : (i) tid a l a ir = 5 0 0 m l., (ii) e x p ir a to r y re se rv e a ir = 1 ,0 0 0 m l. T h e v ita ! c a p a c ity th e r e f o r e c o n s is ts o f: (i) in s p i r a t o r y re se rv e a ir = 2 ,5 0 0 m l. (ii) tid a l a i r = 5 0 0 m l. (iii) e x p i r a t o r y re se rv e a ir = 1 ,0 0 0 m l. 4 ,0 0 0 m l. F a c t o r s d e te r m in in g th e v o lu m e o f th e v ita l c a p a c ity t h e r e f o r e a r e : (i) S ize o f t h e th o r a c ic c a g e (cf. m e n a n d w o m e n ) ; (ii) E x p a n d ib ility o f th e th o r a c ic c a g e , i.e. n o r m a l s t r u c tu r e — a n d f u n c tio n o f its b o n y f r a m e w o r k ; (C o n tin u e d o n P a g e 14). P H Y S I O T H E R A P Y R ep ro du ce d by S ab in et G at ew ay u nd er li ce nc e gr an te d by th e P ub lis he r (d at ed 2 01 3. ) Page 14 P H Y S I O T H E R A P Y September, 1960 A S P E C T S O F R E S P I R A T I O N (C o n tin u e d f r o m P a g e4 ). (iii) S tre n g th (size) o f th e r e s p ir a to r y m u sc le s— i n s p ir a to r y a n d e x p i r a t o r y (cf. th e r e s p ir a to r y m u sc le s o f th e tr a in e d a th le te ) ; (iv) E la s tic ity o f th e lu n g s (cf. th e re d u c e d v ita l c a p a c it y in a ll fo rm s o f fib ro s is o f th e lu n g s ); (v ) F u n c tio n a l e fficien c y o f th e n e r v o u s s t r u c tu r e s c o n ­ c e rn e d : (a ) r e s p ir a to r y c e n tr e , (b ) a n t e r i o r m o t o r n e u r o n s (cf. p o lio m y e litis ), (c) p e r ip h e r a l e ffe re n t o r m o t o r n e rv e s to th e r e s p i­ r a t o r y m u sc le s. W h y d o th e in s p ir a to r y m u sc le s re la x ? B e c a u s e th e y re c e iv e n o im p u lse s f r o m th e s p in a l c o rd m o t o r n e u r o n s , w h ic h in t u r n re c e iv e n o im p u lse s f r o m th e i n s p ir a to r y c e n tre . T h u s , th e c o n t i n u o u s d is c h a rg e o f r e p e titiv e im p u lse s b y th e i n s p ir a to r y n e u r o n s h a s t e m p o r a rily b e e n sto p p e d o r in h ib ite d , o r i n s p ir a tio n h a s b e e n c u t s h o r t to a llo w e x p i r a t i o n to t a k e p la c e . T h e r e s p o n s ib le m e c h a n is m s f o r th is a r e : (i) p n e u m o ta x ic c e n tre , (ii) e x p i r a t o r y c e n tre , (iii) H e r in g - B r e u e r reflex (v a g a l m e c h a n is m ). P n e u m o ta x ic C e n tre . T h is c o n s is ts o f r e s p ir a to r y n e u r o n s s c a tte re d in th e f o r m a tio re tic u la ris o f th e p o n s . T h e y m a k e s y n a p tic a l c o n ta c t w ith th o s e o f t h e i n s p ir a to r y a n d e x p i r a t o r y c e n tre s . A s t h e in s p ir a to r y n e u r o n s d is c h a rg e to t h e a n t e r i o r m o t o r n e u r o n s , th e r e is a s im u lta n e o u s d is c h a rg e to th e p n e u m o ta x ic n e u r o n s . T h e s e in t u r n d is c h a rg e to th e e x p i r a t o r y n e u r o n s . A t a c e r ta in c ritic a l level o f e x c ita tio n , th e l a t t e r e m it a b a r r a g e o f im p u lse s a t th e i n s p ir a to r y n e u r o n s , w h ic h f o r a s h o r t p e r io d , c o m p le te ly in h ib its th e ir d isc h a rg e . H e r in g -B re u e r re fle x . T h e d e lic a te a lv e o la r m e m b r a n e s o f th e lu n g c o n ta in r e c e p to r s s e n s itiv e t o th e a m o u n t o f s tr e tc h o f in f la tio n o f th e lu n g — str e tc h re cep to rs. A s a lu n g b e c o m e s p ro g re s s iv e ly m o r e in fla te d d u r in g in s p i r a t i o n , th e s e re c e p to r s a r e s tim u la te d a n d a s tr e a m o f a ffe re n t im p u lse s is c o n d u c te d a lo n g a ffe re n t v a g u s fib res t o t h e e x p i r a t o r y n e u r o n s , w h ic h a g a in in h ib it th e in s p ir a to r y n e u r o n s , a llo w in g e x p ir a tio n to ta k e p la c e . T h e r h y th m o f b r e a th in g is th e r e fo r e th e re su lt o f th e in te r a c tio n o f th e in s p ir a to r y , e x p i r a t o r y a n d p n e u m o to x ic c e n tre s a n d th e v a g a l m e c h a n is m . W h e r e a s th e d e p th o f a n i n s p ir a tio n is d e te r m in e d b y th e d e g re e o f d is c h a rg e b y th e in s p ir a to r y n e u r o n s t h e ra te o f r e s p i r a t i o n is d e p e n d e n t o n th e a c tiv ity o f th e p n e u m o ta x ic a n d v a g a l m e c h a n is m s . H o w is r e s p ir a tio n re g u la te d ? T h e r e s p i r a t o r y p a t t e r n (i.e. d e p th a n d ra te ) is re g u la te d , v ia th e r e s p ir a to r y c e n tr e , b y : (i) c h e m ic a l s u b s ta n c e s , a n d (ii) n e rv e im p u lse s . C h e m ic a l S u b sta n c e s. U n d e r a ll c o n d itio n s o f n o r m a l, e u p n e ic b r e a th in g , th e r e s p ir a to r y p a t t e r n is r e g u la te d a lm o s t e x c lu s iv e ly b y th e C 0 2 c o n te n t o f th e A r te r ia l blo o d . T h is is m e d ia te d th r o u g h a d ir e c t a c tio n o f th e H C 0 3 ( b ic a r b o n a te ) io n s o n th e r e s p ir a to r y n e u r o n s a n d c h a n g e s in a c id ity ( p H ) c a u s e d b y in c re a se d o r d e c re a s e d C 0 2. T h e n o r m a l te n s io n o f C 0 2 ( p C 0 2) in a r t e r i a l b lo o d = 40 m m . H g . I n c re a s in g th is v o lu m e b y a s little a s 2 m m . H g. is su ffic ie n t to d o u b le p u lm o n a r y v e n tila tio n ( h y p e r p n o e a ) ; h e n c e th e h y p e r p n o e a o f a c id o s is . S im ila rly a slig h t d e c r e a s e o f th is v a lu e c a u s e s a p n o e a ; h e n c e th e slo w sh a llo w b r e a th in g o f a lk a lo s is . In c e r ta in c a s e s o f a n o x ia , th e r e s p ir a to r y p a t t e r n is c o n tr o lle d b y th e 0 2 c o n t e n t ( p 0 2) o f th e a r t e r i a l b lo o d , via th e c h e m o r e c e p to r s o f t h e a o r t i c a n d c a r o t i d b o d ie s . N e rv e Im p u lse s. T h e s e h a v e a lr e a d y b e e n re fe rre d to e ls e w h e re . T h e h y p e r p n o e a o f m u s c u la r a c tiv ity is la rg e ly th e effe ct o f a f fe re n t im p u ls e s f r o m t h e c o n t r a c t i n g m u s c le s a n d m o v in g j o i n t s o f th e r e s p i r a t o r y c e n tre . D u r i n g o t h e r p h y sio lo g ic a l a c tiv itie s , e .g . ta lk in g , sn e e z in g , c o u g h in g , s w a llo w in g , e tc ., th e b a s ic r e s p i r a t o r y p a tte r n (a s c o n tr o lle d b y th e C 0 2— c o n t e n t o f th e a r t e r i a l b lo o d ) is m o d ifie d b y n e rv e im p u ls e s f r o m th e r e sp e c tiv e n e rv e c e n tr e s , a c tin g o n th e n e u r o n s o f th e r e s p ir a to r y c e n tre . P U L M O N A R Y T E S T (C o n tin u e d f r o m P a g e 1). r e d u c tio n o f tim e d v ita l c a p a c ity a n d th e m a x im u m b r e a th in g c a p a c ity . R e s id u a l v o lu m e is u s u a lly c o n s id e r a b ly in c re a se d b o th a s a n a b s o lu te v a lu e a n d a s a p r o p o r t i o n o f th e to ta l lu n g c a p a c ity . C lin ic a l F e a tu r e s . A n a d v a n c e d c a u s e o f e m p h y s e m a w ill th e n b e se e n to h a v e a n o x a e m ia w ith c y a n o s is h e ig h te n e d f re q u e n tly by s e c o n d a r y p o ly c y th a e m ia a n d s h o w s th e c o n s id e ra b le v e n tila to r y d iffic u lty a s s o c ia te d w ith h y p e r in fla tio n o f th e lu n g s a n d d iffu se e x p ir a to r y o b s t r u c t i o n . C lin ic a lly th e p a t i e n t w h e e z e s o n th e slig h te s t e x e r tio n o r e v e n a t r e s t a n d h a s t o u se h is a c c e s s o ry m u s c le s o f r e s p ir a tio n . T h e c h e s t b e c o m e s b a r re l- s h a p e d a n d th e rib s h o r i z o n t a l ly p la c e d . R e s p i r a t io n is c a r r ie d o u t p a r tia lly b y d ia p h r a g m a tic e x c u r s io n a n d “ e n b lo c ” m o v e m e n t o f t h e b a r re l- s h a p e d th o r a c ic c a g e . O n a u s c u la tio n th e p r o lo n g e d e x p ir a to r y d iffic u lty o f a f o rc e d m a x im a l e x p ir a tio n is u s u a lly q u ite e a s ily d e te c te d a n d in m y o p in io n th is is th e m o s t v a lu a b le s in g le sig n in t h e c lin ic a l a s s e s s m e n t o f th e p a tie n t. F o r th e m o s t p a r t a ls o th e r e is r e d u c tio n in a ir e n t r y a s j u d g e d by th e s te th o s c o p e . T re a tm e n t. T r e a t m e n t is d iffic u lt a n d p r o lo n g e d in m o s t in sta n c e s. I t h a s t o b e sa id a t th e o u ts e t t h a t e m p h y s e m a a s su c h c a n n o t b e in flu e n c e d b y t r e a t m e n t a n d a n y th e r a p e u t i c a t t a c k is d ir e c te d a g a in s t b r o n c h o s p a s m , in fe c tio n a n d v isc id se c re ­ tio n s w ith a v a r ie ty o f a g e n ts in c lu d in g a n tib io tic s , a n ti- s p a s m o d ic s , s te ro id s , d e te r g e n t a n d w e ttin g i n h a la n t a n d e n z y m e s ( s tr e p to k in a s e a n d try p s in ). A lth o u g h th e r e is n o t th e s lig h te s t d o u b t in m y m in d th a t P h y s io th e r a p y is o f c o n s id e ra b le v a lu e in m a k in g m o re e fficien t u se o f t h e p a t i e n t ’s n a t u r a l c a p a c ity f o r v e n tila tio n , th e r e is n o o b je c tiv e im p ro v e m e n t in p u l m o n a r y f u n c tio n te s ts in c o n tr o lle d se rie s o f p a tie n ts in w h o m th is h a s b een m e a s u re d b e fo re a n d a f te r p h y s io th e r a p y . C o m p lic a tio n s (e sp e c ia lly b r o n c h o p n e u m o n i a a n d c o r- p u lm o n a le ) a r e o f a s e rio u s n a t u r e a n d r e q u ir e v ig o ro u s t r e a tm e n t in th e ir o w n r ig h t. F r e q u e n tly th e n w e h a v e a p a t i e n t w h o is v e ry ill w ith g ro s s ly re d u c e d r e s p ir a to r y re se rv e a n d c o n s id e r a b le s e c o n d a r y in f e c tio n in th e lu n g s w ith a s s o c ia te d c a r d ia c f a ilu re a n d a w id e , v ig o r o u s a n d p e r s is te n t th e r a p e u t i c a t t a c k is in d ic a te d . A s f a r a s f u tu r e d e v e lo p m e n ts a r e c o n c e r n e d , h o w e v e r, p r e v e n tio n is lik ely to p r o v e m o r e r e w a r d in g th a n a n a t t e m p t a t c u re . R ep ro du ce d by S ab in et G at ew ay u nd er li ce nc e gr an te d by th e P ub lis he r (d at ed 2 01 3. )