Respiratory Investigations and Pulmonary Function Tests Flashcards

Flashcards covering key medical terminology, diagnostic parameters, contraindications, and principles of pulmonary function testing and arterial blood gas analysis based on the lecture.

Peak Expiratory Flow Rate (PEFR)

The maximum speed of airflow generated during forced expiration, used primarily to diagnose occupational asthma, monitor therapeutic response, and predict asthma exacerbations.

$$FEF_{25\%-75\%}$$

The forced expiratory flow occurring during the middle $50\%$ of exhaled volume; an effort-independent measurement that indicates small airway obstruction when reduced below $50\%$ of the predicted mean.

Bronchial Reversibility Test

A diagnostic procedure where spirometry is conducted before and $15\,\text{minutes}$ after bronchodilator administration; an increase in $FEV_1$ by $\ge 12\%$ and $200\,\text{mL}$ confirms asthma.

Bronchoprovocation Testing

A test evaluating airway hyperreactivity (AHR) using provocative agents (e.g., methacholine, histamine) in patients with normal baseline spirometry; a positive result is defined as a drop in $FEV_1$ of $> 20\%$.

Diffusion Capacity ($DL_{CO}$ / $TL_{CO}$)

An investigation measuring gas transfer across the alveolar-capillary membrane using carbon monoxide, which is reduced in emphysema, interstitial lung disease, pulmonary hypertension, and anemia.

Transfer Coefficient ($K_{CO}$)

The carbon monoxide transfer factor per unit lung volume ($TL_{CO}/VA$), used to differentiate intrapulmonary causes of restriction (reduced $K_{CO}$) from extrapulmonary causes (normal or elevated $K_{CO}$).

Arterial Blood Gas (ABG) Analysis

An investigation assessing arterial blood $pH$, $PO_2$, $PCO_2$, $HCO_3^-$, and base excess to determine oxygenation, adequacy of ventilation, and underlying acid-base disorders.

Alveolar-Arterial (A-a) Gradient

The difference between alveolar oxygen partial pressure ($P_A O_2$) and arterial oxygen partial pressure ($P_a O_2$); an elevation above $2\text{ to }4\,\text{kPa}$ ($5\text{ to }20\,\text{mmHg}$) indicates a ventilation/perfusion mismatch or diffusion defect.

Residual Volume (RV)

The volume of air remaining in the lungs after maximal forced expiration, which cannot be measured directly by spirometry and is calculated as $RV = FRC - ERV$.

Functional Residual Capacity (FRC)

The volume of air remaining in the lungs at the end of a normal quiet expiration, measured via closed-circuit helium dilution, open-circuit nitrogen washout, or body plethysmography.

Total Lung Capacity (TLC)

The total volume of air present in the lungs after a full maximal inhalation.

Vital Capacity (VC)

The maximum volume of air that can be exhaled following maximal inhalation, represented mathematically as $VC = IRV + TV + ERV$.

Pulse Oximetry

A noninvasive method used to monitor peripheral blood oxygen saturation ($SpO_2$), which can be inaccurate in hypothermia, shock, carbon monoxide poisoning, methemoglobinemia, or bright ambient light.

Obstructive Lung Defect

A pattern on spirometry characterized by a reduced $FEV_1/FVC$ ratio ($< 70\%$ or below the lower limit of normal), characteristic of diseases like asthma, COPD, and bronchiectasis.

Restrictive Lung Defect

A pattern on lung function testing defined by a reduced Total Lung Capacity ($TLC$) and reduced Forced Vital Capacity ($FVC$) with a normal or elevated $FEV_1/FVC$ ratio.

Total-Body Plethysmography

The fastest diagnostic technique used to measure Functional Residual Capacity ($FRC$) and determine absolute lung volumes that cannot be directly measured by spirometry.