RT Book, Section
A1 Carreon, Megan L.
A1 Velez, Maria I.
A1 Levine, Stephanie M.
A1 Peters, Jay I.
A2 DiPiro, Joseph T.
A2 Yee, Gary C.
A2 Haines, Stuart T.
A2 Nolin, Thomas D.
A2 Ellingrod, Vicki L.
A2 Posey, L. Michael
SR Print(0)
ID 1206030389
T1 Evaluation of Respiratory Function
T2 DiPiro’s Pharmacotherapy: A Pathophysiologic Approach, 12th Edition
YR 2023
FD 2023
PB McGraw Hill
PP New York, NY
SN 9781264264544
LK accesspharmacy.mhmedical.com/content.aspx?aid=1206030389
RD 2024/04/19
AB KEY  CONCEPTS  The  function  of  the  lungs  is  to  maintain  the  arterial  partial  pressure  of  oxygen  (PaO2)  and  arterial  partial  pressure  of  carbon  dioxide  (PaCO2)  within  normal  ranges  (ie,  normal  ventilation-perfusion  ratio).  The  air  in  the  lung  is  divided  into  four  compartments:  tidal  volume—air  exhaled  during  non-exertional  breathing;  inspiratory  reserve  volume  (IRV)—maximal  air  inhaled  above  tidal  volume;  expiratory  reserve  volume  (ERV)—maximum  air  exhaled  after  tidal  volume;  and  residual  volume  (RV)—air  remaining  in  the  lung  after  maximal  exhalation.  The  sum  of  all  four  components  is  the  total  lung  capacity  (TLC).  Pulmonary  function  tests  will  produce  values  consistent  with  normal  lungs  or  an  obstructive  or  restrictive  disease:  recognition  of  these  values  is  key.  Obstructive  lung  disease  is  defined  as  an  inability  to  get  air  out  of  the  lungs.  It  is  identified  on  spirometry  when  forced  expiratory  volume  in  the  first  second  of  expiration  (FEV1)  compared  to  the  forced  vital  capacity  (FVC)  (total  amount  of  air  that  can  be  exhaled  during  a  forced  exhalation)  (FEV1/FVC)  is  less  than  70%  to  75%  (0.70-0.75)  in  adults  (or  below  the  lower  limit  of  normal  [LLN]  based  on  population  studies).  An  increase  in  FEV1  of  12%  (and  greater  than  0.2  L  in  adults)  after  an  inhaled  β-agonist  suggests  an  acute  bronchodilator  response.  Restrictive  lung  disease  is  defined  as  an  inability  to  get  enough  air  into  the  lung  and  is  best  defined  as  a  reduction  in  TLC  (usually  less  than  80%  of  predicted).  Restrictive  lung  disease  can  be  produced  by  a  number  of  diseases,  such  as  increased  elastic  recoil  (interstitial  lung  disease),  respiratory  muscle  weakness  (myasthenia  gravis),  and  mechanical  restrictions  (pleural  effusion  or  kyphoscoliosis).  It  can  also  be  the  result  of  poor  effort  during  a  pulmonary  function  test  (PFT).  The  shape  of  the  flow-volume  loop,  which  includes  inspiratory  and  expiratory  flow-volume  curves,  and  the  ratio  of  forced  expiratory  and  inspiratory  flow  at  50%  of  VC  (FEF50%/FIF50%  greater  than  1)  may  be  useful  in  the  diagnosis  of  upper  airway  obstruction.  Cardiopulmonary  exercise  testing  allows  for  the  assessment  of  multiple  organs  involved  in  exercise.  Spirometry  and  other  pulmonary  function  tests  in  children  are  possible  and  can  successfully  be  done  with  proper  coaching  methods  and  modified  reference  values.