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CHANGES IN VENTILATION

MODIFY ALVEOLAR GAS COMPOSITION

IN THE HUMAN RESPIRATORY SYSTEM

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Introduction

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Respiration is vital for homeostatic maintenance, allowing intracellular metabolic processes to produce energy by providing oxygen (O2) and removing carbon dioxide (CO2). Ventilation is ... Air is inspired or breathed ... (Sherwood, 2007) from the lungs into the external environment. Oxygen is stored as haemoglobin; CO2 is stored as ... To supply cells with oxygen, inspired air undergoes gas exchange in alveolar sacs (Figure 1. Sherwood, 2007), small grape-like structures that branch ... following Frick's law of diffusion (Appendix).

Figure 1- The respiratory pathway. Oxygen and carbon dioxide are transported from the lungs, via circulation to fuel oxidation in tissues.

Capillaries surround alveoli for rapid and effective exchange. To protect alveoli and maintain their structure, lungs never deflate completely, maintaining a ... (Sherwood, 2007). During inspiration the first gas to enter alveoli is ... Therefore changes in alveolar gas composition (most significantly O2 and CO2) reflect a disturbance in ventilation. The aim of this experiment is to determine the effects of ventilation on alveolar gas composition.

It is hypothesised that stopping ventilation will alter .... During normal breathing, PO2 ... If ventilation is obstructed (breath-holding), PO2 ... After over-breathing, when the rate of ventilation exceeds the metabolic requirements for CO2 removal (Sherwood, 2007), PO2 will be ... If breath-holding occurs after hyperventilation, excess O2 is metabolised causing ... After this period, PCO2 ...

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Methods

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Apparatus was set-up to measure PCO2 and PO2 (mmHg) from the end of the volume of air leaving the lungs in a single breath, the end tidal volume (Sherwood, 2007) of a subjects' expiration (figure 2). Software displayed the gas composition.

After recording the values following a normal exhalation, ventilation was manipulated ... Firstly, the subject ... At the end of expiration, the gas composition was ... Secondly, the subject .... For the third manipulation, the subject was instructed .... The length of breath hold was timed then gas composition measured at the end of expiration.

Results

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Normal PO2 at 116 mmHg was triple PCO2 at 40 mmHg (figure 3). Breath-holding decreased PO2 to ... Conversely, over-breathing ... After over-breathing, the length of breath-hold ...

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(figure not included)

Figure 4- Mean length of breath-hold with one standard deviation.

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Discussion

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Experimental results were consistent with theoretical values and hypotheses, all ventilation modifications caused changes in alveolar gas composition. The PO2 result for normal breathing was ... During breath-hold, oxygen was metabolised and ...

After over-breathing, PO2 was ... When breath was held after a period of hyperventilation, ... At the end of this period, PCO2 ... These changes could be related to ... If PO2 drops below 60 mmHg it, rather than CO2, becomes .... In both cases of breath-holding, PO2 was ... As neither physiological stimulus to breathe was approached, termination ... .

Several factors were kept constant including .... With only six subjects, ... (Appendix). Both breath-holding sections showed large ... (Appendix). Inconsistencies between experimental and expected data could have reflected ... The method is inherently subjective, ... Future experimentation could ...

Therefore changes in ventilation significantly change alveolar gas composition. When ventilation is obstructed, ... When ventilation is excessive ...

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References

  1. Discipline of Physiology. 2007. Integrated Physiology 2006 and Integrated Physiology (Advanced) 2906 Practical Guide, Semester 2. The University of Sydney Publishing Service
  2. Sherwood, L. 2007. Human Physiology � From Cells to Systems. Thompson Brooks/Cole. Australia.

Appendices

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