L17 Lab Tests (Asthma)

Pneumonia will affect the gas exchange because it affects the alveolar spaces.

Alveolar ventilation (Av) allows gas to move from the lungs to blood. An adequacy of [blank_start]capillary[blank_end] flow to the lungs is required for adequate [blank_start]gas[blank_end] exchange. When the capillary flow is compromised, a mismatch will occur between [blank_start]Av and perfusion[blank_end]. (I.e. even when alveolar ventilation is fine, if blood flow to the alveolar capillaries is poor the perfusion of gasses will be [blank_start]poor[blank_end].) Factors that affect pulmonary capillary flow include: - pulmonary [blank_start]embolism[blank_end] - right [blank_start]ventricular[blank_end] dysfunction

When PaCO2 gets high we breathe slower.

Spirometry tests assess alveolar ventilation. A FEV/FVC (Forced Expiratory Volume (1s) & Forced Vital Capacity) ratio is usually [blank_start]0.8[blank_end]. Peak expiratory flow rate (L/min) values of PEFR depend on size, sex and age, but typically a healthy range for adults is [blank_start]400 - 600[blank_end] L/min. PEFR tends to be less [blank_start]sensitive[blank_end] to small airways disease. Obstructive diseases ([blank_start]asthma, COPD, bronchitis[blank_end]) reduce the expiration ability (reduce [blank_start]FEV1[blank_end] and [blank_start]FEV/FVC[blank_end] ratio.) There is evidence of [blank_start]reversibility[blank_end]. Restrictive diseases ([blank_start]fibrosis[blank_end], end stages of [blank_start]COPD[blank_end]) reduce the usable capacity (reduce [blank_start]FVC[blank_end], and [blank_start]reduce[blank_end] FEV.)

Partial pressure of oxygen & carbon dioxide: 1. PaO2, partial pressure of oxygen in the arterial circulation - PaO2 is dependent on [blank_start]inspired[blank_end] O2 and [blank_start]atmospheric[blank_end] pressure. - Values [blank_start]< 60 mmHg[blank_end] typically cause symptoms. 2. PaCO2, partial pressure of CO2 in the arterial circulation - Normal value is [blank_start]40 mmHg[blank_end] - It is produced by [blank_start]tissues[blank_end] during internal respiration - Values [blank_start]> 50 mmHg[blank_end] typically cause symptoms