2 December 2009 Respiratory Physiology Lab this week: A case study and measuring lung volumes and capacities with Powerlab. Bring calculator and textbook to lab. About the Final Exam….. Choice of Tuesday or Wednesday 9-noon Details of format and suggestions to be posted to website.

Figure 13.19 Tidal inspiration At end of normal tidal expiration

V = VT x f VA = (VT – VDS) x f Anatomic dead space = air remaining in conducting zone (typically 150 ml.) What is VA if Tidal Volume is 150 ml?

Gas Laws Dalton’s Law Henry’s Law Total pressure = sum of partial pressures PATM = P N2 + P O2 + P CO2 100% = 79% + 21% + <1% P O2 = 0.21 x 760mmHg = 160 Partial pressure of Oxygen in atmosphere at sea level is 160 mmHg N2 is physiologically inert; ignore Gases dissolve in liquids in proportion to their partial pressure in the air in contact with that liquid air P O2 =160 mmHg blood P O2 =160 mmHg

CO2 production O2 uptake

CO2 production = Respiratory Quotient O2 uptake = 0.8 for proteins = 0.7 for fat = 1.0 for carbohydrates =0.8 for mixed diet 200 mlCO2/min 250 ml O2/min

Gas exchange All gases move by diffusion. Thus limited by: Surface area Distance Concentration gradient In the lung, gases must move from air to water and vice versa. The amount is proportional to Solubility (CO2 more soluble that O2) Temperature (colder fluids dissolve more gas) Pressure gradient

Pathological limitations to diffusion

Alveolar to arterial gradient is due to ventilation/perfusion inequality. Ventilation by Bulk Flow Pulmonary Venous blood is equivalent to Systemic Arterial blood. Gas exchange Gas exchange Gradient for CO2 is only 6 mmHg; CO2 is more soluble and permeable than O2

Landmark numbers to memorize.

Matching blood flow (Q, also called “perfusion” ) to ventilation (V) by pulmonary arterioles that constrict in response to low O2 and dilate in response to hi O2 (Note this response to O2 is opposite that of systemic arterioles!) Thus, poorly ventilated regions of the lung will receive less blood flow. So…. Q is “matched” to V, but not perfectly.

Carbon dioxide transport carbaminohemoglobin Chloride Shift CA = carbonic anhydrase Hb is a Buffer Carbon dioxide transport

Figure 13.31 Hb can bind O2, CO2, and H+ Increases in CO2 and H+ decrease the affinity of Hb for O2

Figure 13.27 CO2 and O2 bound to Hb do not contribute to partial pressure (no longer a dissolved gas!)

Oxygen exchange

Table 13.08

Steep Flat