Materials & Methods Discussion Introduction Results

Does  Diurnal  Variation  in  Cough  Reflex   Testing  Exist  in  Healthy  Young  Adults?     1,2 1,2 S.  Davies ,  M-­‐L.  Huckabee    

1The  University  of  Canterbury  Rose  Centre  for  Stroke  Recovery  and  Research,2Department  

of  Communication  Disorders,  University  of  Canterbury,  Christchurch,  New  Zealand  

Introduction   Ê  C ough   reflex   testing   (CRT)   is   increasingly   utilised   in   dysphagia   research   and   clinical   practice   to   assess   reflexive   cough    

sensitivity  and  silent  aspiration  risk.  Diurnal  variation  in  cough  sensitivity  may  be  a  major  confounding  variable1  that  is   controlled  for  in  clinical  trials  by  testing  at  the  same  time  each  day.  However,  this  may  not  be  feasible  in  acute  clinical   settings.   Diurnal   variation   has   only   been   described   in   CRT   using   a   vital-­‐capacity   method.   Our   aim   was   to   investigate   diurnal  variability  in  CRT  in  healthy  young  adults  using  a  tidal-­‐breathing  method.  

     

Materials  &  Methods   Ê 53   participants   (27   male,   age   range   19   –   37   years)   underwent   CRT   both   in   the   morning  

(between   9am   –   midday)   and   the   afternoon   (between   2   –   5pm).   The   order   of   testing   was     randomised.       Ê CRT  was  performed  using  nebulised  citric  acid  presented  via  facemask.        Ê Participants  were  instructed  to  “keep  breathing;  try  not  to  cough”.  Suppressed  cough  threshold   2   was  chosen  to  represent  a  true  cough  reflex .      Ê Citric   acid   was   presented   starting   at   0.1   mol/L   and   increasing   in   0.1   mol/L   increments   up   to     1.2mol/L.  The   lowest   concentration   of   citric   acid   that   elicited   a   cough   response   on   2/3   trials     was  considered  to  be  the  CRT  threshold.       Ê To  facilitate  participant  blinding,  saline  was  interspersed  randomly  throughout  testing.      

 

Results  

   

 

Ê    Morning  cough  reflex  thresholds  (Mdn    =  0.4  mol/L)  were  

not   significantly   different   from   afternoon   cough   reflex     thresholds  (Mdn  =  0.4  mol/L),  p  >  .05,  T  =  11,  r  =  -­‐.14.      

 

first  test  (Mdn  =  0.3  mol/L)  were  significantly  lower  than  the   second  test  (Mdn  =  0.5  mol/L),  p  <  .01,  T  =  6,  r  =  0.27.    

Overall  cough  reflex  thresholds  at  different  times  of  day   0.6   0.5   0.4  

0.4  

0.4  

0.3   0.2   0.1  

Cough  reflex  thresholds:  first  test  vs.  second  test   Median  cough  reflex  threshold  (mol/L)  

Median  cough  reflex  threshold  (mol/L)  

 

Ê Regardless   of   time   of   day,   cough   reflex   thresholds   from   the  

0.6  

p  <  .01   0.5  

0.5   0.4   0.3  

0.3  

0.2   0.1   0  

0   Morning  

First  Test  

Afternoon  

Second  Test  

Discussion   Ê There   is   no   evidence   for   diurnal   variability   in   CRT   using   a   tidal   breathing   method.  There   is,   however,   an   order   effect  

irrespective  of  time  of  day,  confirming  that  healthy  participants  are  able  to  volitionally  modulate  their  cough.   Ê In  our  young,  healthy,  participants  this  order  effect  was  greater  than  one  dose  above  initial  thresholds.   Ê Translating   these   findings   to   clinical   practice;   clinicians   should   interpret   the   results   of   repeated   cough   reflex   tests   with   caution.       1Pounsford  JC,  Saunders  KB.  Diurnal  variation  and  adaptation  of  the  cough  response  to  citric  acid  in  normal  subjects.  Thorax.  1985  Sep;40(9):657–61;  2Hegland  et  al.  Volitional  control  of  reflex  cough.  

Journal  of  Applied  Physiology.  2012;  113(1):39-­‐46