Mammalian Physiology
Respiration Physiology

1) Response to high altitude

Simulate ascent to Mt. McKinley (approx. 12,500 ft., see West fig. 9.2 attached) by adjusting the barometric pressure (use 'List All Variables') to 480 mmHg. Run your experiments for a full 10 days (10D) printing out either every half day or as appropriate. If you need to run more than one simulation, in this or any part of this lab, always <Start Over> to avoid cumulative effects.

a) Briefly characterize acid-base (& blood gas/ventilatory) response (as was done in lab last week)

b) Characterize the development of polycythemia (West pg 120-1) by tracking in your tables variables related to erythropoeisis (red blood cell production), red blood cell count and hemoglobin production (use 'List All variables' in conjunction with Find... to locate appropriate variables). If you need to run more than one simulation, in this or any part of this lab, always <Start Over> to avoid cumulative effects.

2) Control of ventilation by PC02A (alveolar PCO2)

a) Evaluate how closely HUMAN follows the normoxia (PO2A = 110 mmHg) curve seen in West Figure 8-4 by creating PCO2A's in the range found in that study by
1)raising FCO2AT to appropriate values.
2) Lower PC02A by lowering basal metabolic rate (BMRB) thereby lowering C02 production (CO2 expired).
(see next page for 'advice' on these maneuvers) If you need to run more than one simulation, in this or any part of this lab, always Start Over to avoid cumulative effects.

b) Extra credit- Figure 8-4 shows the same response for normoxic (=110 mmHg) and hyperoxic (169 mmHg) situations. Test this in HUMAN by raising the fractional concentration of O2 in the breathing mixture to achieve a hyperoxia (increases in P02A ) and evaluate 2 or more of the points you tested above for an effect of hyperoxia on ventilation at a given PC02A.

Overview of creating a range of PCO2

- To achieve above normal pCO2’s you will raise the CO2 fractional concentration in the air ventilated by the model (FCO2AT)* . Higher FCO2AT levels naturally result in higher arterial PCO2 values.

- To achieve below normal pCO2A’s, you will lower the CO2 production rate (basal metabolic rate) of the model. You must resort to lowering CO2 production because normal FCO2AT is already zero at baseline (i.e. atmospheric air normally has virtually no CO2 in it) making it quite impossible to lower it any further.

A] Increasing pCO2 levels

Once you have established new table values for your subject continue for a 1 hour interval after having him/her breathe 1% CO2 by changing the parameter of fractional CO2 (FCO2AT) in the atmosphere. FCO2AT may range in value from 0.0 (0% CO2, the ‘normal’ value) to 1.0 (100% CO2). Think about what value of FCO2AT you would assign to obtain a 1% CO2 breathing mixture (Hopefully, you answered 0.01). Watch the changes in the above (tabular) physiological variables for one hour and record the values at that time. Restart your simulation and repeat the procedure four more times, each at an increasing level of CO2, each time recording at 1 hr. obtaining points to cover the range in West figure 8-4 for the P02 = 110 curve.

[Important: For each new FCO2AT start with a new subject . Experiment #10 has some helpful beginning Tables]

You now have 4-5 pCO2 values in the range of West 8-4 and their corresponding lung ventilations.

B] Decreasing pCO2 levels below normal

It is impossible to lower the atmospheric CO2 below zero. Therefore, to achieve subnormal pCO2 values we resort to a different tactic, lowering CO2 production (i.e. lowering metabolism)

Design an experiment where the blood levels of CO2 are lowered by decreasing the basic level of basal metabolism (BMRB) and therefore the CO2 production rate. Obtain 3 sets of values for various lower levels of CO2 down to values slightly lower than those obtained in Figure 8-4 for the O2=110 curve. Since your objective here is to lower pCO2, 'eyeball' the PCO2 values resulting from your decreases in BMRB for significance. Certainly, they should each be at least 1-2 mmHg or more pCO2 below each preceding higher value.

The overall experimental objective is to achieve a total of 8 or more different levels of blood pCO2 , 5 higher than normal, 3 noticeably lower, and record the level of ventilation associated with each.