Overview
This lecture covers the physiology of respiration, types of breathing, measurement methods, respiratory cycle, lung volumes, pressures, and the impact of various factors on breathing.
Physiology of Respiration
- Respiration involves inhaling oxygen and exhaling carbon dioxide as a waste product.
- Two types of inspiration: quiet (normal) and forced (active).
- Two types of expiration: passive (elasticity/gravity) and active (muscle effort).
- Active expiration compresses the abdomen and reduces thoracic size to expel air.
Measurement of Respiration
- A spirometer measures respiration volume.
- A manometer measures pressure within the respiratory system.
Stages of Respiration and Gas Exchange
- Ventilation: movement of air into respiratory passageways.
- Distribution: air spreads throughout the alveoli.
- Perfusion: movement of fluid through a barrier in the lungs.
- Diffusion: gas exchange across the alveolar-capillary membrane.
Respiratory Cycle and Volumes
- One respiratory cycle = one inspiration + one expiration.
- Adults average 12–18 cycles per minute; newborns 40–70 per minute.
- Quiet tidal respiration is normal, restful breathing (approx. 500 mL air per cycle).
- Alveoli increase from 25 million at birth to 300+ million by age eight.
- Adults retain residual air; infants lack this reserve.
Lung Volumes and Capacities
- Volumes measured in liters (L), milliliters (mL), and cubic centimeters (cc).
- Tidal volume: amount of air inhaled or exhaled during a normal cycle.
- Inspiratory reserve volume: extra air inhaled after a normal inspiration.
- Expiratory reserve volume: extra air exhaled after a normal expiration.
- Residual volume: air remaining after maximum exhalation (about 1.5 L in adults).
- Dead space air: air in passages not involved in gas exchange (about 150 cc).
- Capacities combine volumes; include vital capacity, functional residual capacity, total lung capacity, and inspiratory capacity.
Factors Affecting Respiration
- Exercise, age, illness, and muscle weakness affect breathing.
- Lung capacity remains constant but functional levels decrease with age.
- Vital, inspiratory, and expiratory reserve capacities decrease with age; functional residual capacity increases due to loss of inspiratory capacity.
Respiratory Pressures
- Five types: intraoral (mouth), subglottal (below vocal cords), alveolar (within alveoli), intrapleural (between pleural membranes), and atmospheric.
- Speech requires 3–5 cm H₂O subglottal pressure; conversational speech uses 7–10 cm.
- Pressure rapidly changes to add syllabic stress.
Posture and Speaking
- Reclining decreases resting lung volume and increases breathing effort.
- Normal breathing: inspiration = 40% of cycle, expiration = 60%.
- During speech: inspiration = 10%, expiration = 90%.
- Checking action uses muscles to control expiration for speech.
Key Terms & Definitions
- Inspiration — Breathing in (inhalation).
- Expiration — Breathing out (exhalation).
- Spirometer — Device for measuring volume of air inspired or expired.
- Manometer — Device for measuring pressure.
- Tidal Volume — Air volume moved during a normal breath.
- Residual Volume — Air left in lungs after maximum exhalation.
- Vital Capacity — Max air exhaled after max inhalation.
- Subglottal Pressure — Air pressure below vocal cords.
- Alveoli — Air sacs for gas exchange in the lungs.
- Dead Space Air — Air not involved in gas exchange.
Action Items / Next Steps
- Review chapter sections on lung volumes and capacities.
- Practice exercises for inspiratory and expiratory reserve volumes.
- Visit the provided link on breathing types (not on quiz).
- Be familiar with all bolded terms and their definitions.