3) Airway Resistance
Flow of air, like blood is affected by resistance in the airways . Any condition that narrows or obstructs the airways increases resistance so that more pressure is required. Example: Chronic Obstructive Pulmonary Disease such as emphysema or chronic bronchitis.
Lung Volumes and Capacities
Tidal Volume : the volume of air in one breath (4500 ml/breath)
Respiratory Rate : the amount of air inhaled and exhaled each minute, # of breath/min. (12 breaths/min)
Minute Ventilation (MV) = Respiratory Rate X Tidal Volume
At rest a healthy adult horse averages (8-16) 12 breaths per minute with each inhalation and exhalation moving about 4-5 L of air in or out of the lungs. During exercise those numbers may reach 120 breaths per minutes moving up to 12-15L of air per breath.
MV = 12 breaths/minute X 4500 mL/breath
MV = 54,000mL/min (54 L/min)
Tidal volume may vary from horse to horse and roughly only 70% of it actually reaches the respiratory zone of the respiratory system. The other 30% remains in the conducting airways of the nose, pharynx, larynx, trachea, bronchi, bronchioles, and terminal bronchioles. Air that does not undergo respiratory exchange is known as Anatomical Dead Space . Therefore, not all of the minute ventilation can be used for gas exchange because some of it remains in the anatomical dead space. Inspiratory Reserve Volume: Horses can exceed 4500mL with a deep breath, the additional inhaled air is called inspiratory reserve volume.
Expiratory Reserve Volume : Exhalation forcefully after a normal inhalation
Inspiratory Capacity : the sum of tidal volume and inspiratory reserve
Vital Capacity : the sum of inspiratory reserve volume, tidal volume, and expiratory reserve volume
Residual Volume: the amount of air left in the lungs after forceful exhalation.
Functional Residual Capacity : the sum of residual volume and expiratory reserve volume
Total Lung Capacity : sum of vital capacity and residual volume
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