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Respiration at Rest:

* PaO2 100 mmHg Pulmonary vein (WNL)

* PaO2 40 mmHg Pulmonary artery

* Cardiac Output (Q): SV x HR = 5 L/min

* Low O2 demand

* Low CO2 production

* V/Q Ratio:

- Middle pulmonary aa ~ 0.8, basilar >0.8, apical <0.8

- V/Q ratio is higher when there is less perfusion, ultimately the trachea is considered dead space because of the non-existent perfusion. Inversely, shunt would be 100% perfusion, but no ventilation to the alveoli. In between is the ratios that are more closely considered.

- High V/Q = high oxygenation, low perfusion, less dilated pulmonary capillary sphincter.

- Low V/Q = low oxygenation, high perfusion, more dilated pulmonary capillary sphincter.

V/Q mismatch: units that are high and low, most common cause of hypoxemia (ie COPD, PE, pneumonia)

* The Low V/Q area typically has higher amounts of blood flow leading creating a stronger gradient in when mixed with highly saturated blood, ultimately decreasing the oxygenation of the blood returning to the L-atria.

*When higher amounts of FiO2% are given this creates an externally controlled bias towards better O2 blood saturation.


Respiration during Vigorous Exercise:

* PaO2 100 mmHg Pulmonary vein (WNL)

* PaO2 40 mmHg Pulmonary artery?

* Cardiac Output (Q): SV x HR = 30 L/min (6 x rest value)

* High O2 demand

* High CO2 production


Systemic Exercise Compensations:

Neurological Compensations:

1. Pulmonary Neural Drive via collateral axons of UMN - directly related to motor recruitment

Pulmonary Compensations:

  1. Increased Tidal Volume

  2. Increased Respiratory Rate

Cardiac Compensations:

  1. Increased HR leading to increased Cardiac Output

Vascular Compensations:

  1. Apical, middle, basilar ventilation perfusion ratio uniform conformity to about 80%

  2. Occurs via pulmonary capillary sphincter dilation.

  3. Small PaCO2 drive decreasing pH, shifting disassociation curve right -->



Figure 1:




* How long does it take for stroke volume adaptations to occur?

* Mechanisms of pathology in pulmonary diseases?

Pathological Responses to Ventilation Perfusion Ratio:



References: *****







Stroke Volume:


Additional Sources: arterial signaling - Exercise blood flow - Exercise blood flow 2 - Cell signaling exercise blood flow - Regulation of microcirculation - *microcirculation regulation - * control of blood flow microcirculation,the%20inspiratory%20limb%20of%20ventilators

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