Resp physiology Flashcards
Draw lung volumes
TV: 500ml. normal breath RV: 1500ml. Left after max expiration ERV: 1500ml. Max expiration FRC: 3000ml. RV + ERV IRV: 2500ml. Max inspiration VC: 4500ml. IRV + TV + ERV TLC: 6000ml Closing volume: vol above residual volume when small airways close Closing capacity: lung capacity when small airways close. RV + CV
Draw spirometry traces
5 L expired volume against time. 1 sec for FEV1 normal: FVC 5L, FEV1 3375ml. 75% obstructive: FVC 3L FEV1 1L. 33% restrictive: FVC 3.5L FEV1 3L. 85%
Draw flow volume loops
Y axis -8, -4, 0, 4, 8 Flow rate l.s-1 x axis Vol. TLC and RV normal: expiration reaches 8 then falls. dynamic compression of airways gives concave. insp 4-6 obstructive: decreased PEFR, Increased RV (gas trapping) Decrease flow rates in expiration. Increase concave due ti airway obstruction. insp limb not affected Restrictive: Decrease TLC, Preserved RV, decreased PEFR, Decreased TLC Variable intrathoracic obstruction: Pos P during expiration exacerbates obstruction. TLC and RV unaffected. normal inspiration Variable extrathoracic obstruction: Pos P during expiration opens airways. Inspiration collapses, Inspiration reduces. TLC and RV unaffected Fixed airway obstruction: peak flow dependent on size of orifice. TLC and RV unaffected
West zones
Zone 1: PA>Pa>Pv Zone 2: Pa>PA>Pv Zone 3: Pa>Pv>PA
Derive the Bohr equation
Ratio of physiological dead space to tidal volume
30% (0.3)
VD/VT = (PACO2-PECO2)/PaCO2
FE x VT=(Fi x FD) + (FA[VT-VD])
Fi = 0
FE x VT=(FA[VT-VD])
FE x VT = (FA x VT) - (FA x VD)
FA x VD = (FA x VT) - (FE x VT)
Divide by VT
(FA x VD) / VT = FA - FE
Divide by FA
VD / VT = (FA - FE) / FA
Describe Fowler’s method
Anatomical dead space
Single vital capacity breath 100% 02
Nitrogen on y axis
4 phases:
1: pure dead space
2: mix dead space/alveolar gas. area a/b
3: plateau. steady N2
4: upstroke closing volume. as not diluted by 02 during 1st breath
Describe V/Q mismatch
alveolar ventilation 4.5L/min, pulmonary arterial flow 5L/min
V/Q 0.9
Both V/Q increase from top to bottom but perfusion more than ventilation
Alveolar Gas equation
PA02 = [Fi02 x (Patm - PH20) - (PaCO2/R)
PA02 = [0.21 x (101.3 - 6.3)] - (5.3/0.8)
PA02 = (0.21 x 95) - 6.6
PA02 = 19.95 - 6.6
PA02 = 13.35
R: fat 0.7, normal 0.8, carb 1
Derive the shunt equation
QT= total blood flow
QS = shunted blood
CcO2 = end capillary blood flow
CvO2 = shunted blood
CaO2 = arterial blood
QT.CaO2 = (QS. CV02) + [(QT - QS) x (CcO2)]
QT.CaO2 = (QS. CV02) + (QT. Cc02) - (QS. Cc02)
(QS. Cc02) = (QS.CvO2) + (QT.Cc02) - (QT.Ca02)
(QS. Cc02) - (QS.CvO2) = (QT.Cc02) - (QT.Ca02)
Qs(Cc02 - CvO2) = QT (CcO2 - CaO2)
Define Hypoxia
Insufficient supply of oxygen to tissues to maintain normal cellular function
Hypoxaemic hypoxia:
Reduction in partial pressure of 02 in blood: V/Q
Anaemic:
Insufficient oxygenation due to failure of oxygen carrying capacity: carbon monoxide
Ischaemic:
Failure of perfusion: septic shock
Histotoxic:
Failure of oxidative phosphorylation: Cyanide
Hypoxaemic hypoxia
Reduction in partial pressure of 02 in blood: V/Q
Anaemic hypoxia:
Anaemic:
Insufficient oxygenation due to failure of oxygen carrying capacity: carbon monoxide
Ischaemic:
Ischaemic:
Failure of perfusion: septic shock
Histotoxic:
Histotoxic:
Failure of oxidative phosphorylation: Cyanide
Oxygen delivery and transport
Air: P02 = FI02. Patm
Trachea: Humidification. P02 = FI02 (Patm-Ph20)
Alveolus: Ventilation. PA02 = [Fi02 (Patm - PH20)] - (PC02/R)
Capillary: Diffusion. Negligible for 02
Artery: Shunt, V/Q mismatch. A-a
Mitochondria: Low 02 around 1.5kPa
Veins: 6.3kpa
