Because of difference between atmospheric and

This preview shows page 7 - 9 out of 12 pages.

Because of difference between atmospheric and intrapulmonary pressure, air flows into lungs, down its pressure gradient, until Ppul = Patm During same period, Pip lowers to about 6 mm Hg less than Patm - Forced (deep) inspirations can occur during vigorous exercise or in people with COPD - Accessory muscles are also activated Scalenes, sternocleidomastoid, and pectoralis minor; erector spinae muscles of back also help to straighten thoracic curvature Act to further increase thoracic cage size, creating a larger pressure gradient so more air is drawn in Expiration - Quiet expiration normally is passive process Inspiratory muscles relax, thoracic cavity volume decreases, and lungs recoil Volume decrease causes intrapulmonary pressure (Ppul) o increase by +1 mm Hg Ppul > Patm so air flows out of lungs down its pressure gradient until Ppul = Patm - Forced expiration is an active process that uses oblique and transverse abdominal muscles, as well as internal intercostal muscles Nonrespiratory air movements - Many processes can move air into or out of lungs besides breathing - May modify normal respiratory rhythm - Most result from reflex action, although some are voluntary - Examples: coughing, sneezing, crying, laughing, hiccups, and yawns Assessing Ventilation
Several respiratory volumes can be used to assess respiratory status Respiratory volumes can be combined to calculate respiratory capacities, which can give information on a person’s respiratory status Respiratory volumes and capacities are usually abnormal in people with pulmonary disorders Spirometer: original, cumbersome clinical tool used to measure patient’s respiratory volumes - Electronic measuring devices used today Respiratory Volumes Tidal volume (TV): amount of air moved into and out of lung with each breath - Averages ~ 500 mL Inspiratory reserve volume (IRV): amount of air that can be inspired forcibly beyond the tidal volume (2100- 3200 mL) Expiratory reserve volume (ERV): amount of air that can be forcible expelled from lungs (1000-1200- mL) Residual volume (RV): amount of air that always remains in lungs - Needed to keep alveoli open Respiratory Capacities Combinations of two or more respiratory volumes - Inspiratory capacity (IC): sum of TV + IRV - Functional residual capacity (FRC): sum of RV + ERV - Vital capacity (VC): sum of TV + IRV + ERV - Total lung capacity (TLC): sum of all lung volumes (TV + IRV + ERV + RV) Dead Space Anatomical dead space: does not contribute to gas exchange - Consists of air that remains in passageways; ~ 150 mL out of 500 mL TV Alveolar dead space: space occupied by nonfunctional alveoli - Can be due to collapse or obstruction Total dead space: sum of anatomical and alveolar dead space Alveolar Ventilation Minute ventilation: total amount of gas that flow into or out of respiratory tract in 1 minute - Normal at rest = ~ 6 L/min - Normal with exercise = up to 200 L/min - Only rough estimate of respiratory efficiency Alveolar ventilation rate (AVR): flow of gases into and out of alveoli during a particular time - Better indicator of effective ventilation

  • Left Quote Icon

    Student Picture

  • Left Quote Icon

    Student Picture

  • Left Quote Icon

    Student Picture