Physiology of Respiration

Overview Boyle’s law Passive and active respiration Torque, elasticity, and gravity Volumes and capacities Pressures Posture and lung volume Muscle activity during speech

Respiration and Boyle’s Law

Respiration The exchange of gas between an organism and its environment. Inspiration: Drawing air into the respiratory system. Expiration: Process of evacuating air from the lungs during respiration.

Boyle’s Law Boyle’s Law: Given a gas of constant temperature, as volume is increased, pressure will decrease. Air pressure: Force exerted on walls of a chamber by molecules of air. Natural law states that air will flow to equalize pressure.

When volume goes down air pressure goes up if air particle is constant When volume goes down air pressure goes up if air particle is constant. More air means more air pressure if volume is the same. Rarefication when air particles are low.

Boyle’s Law Positive pressure: Produced by: Adding air particles to a fixed volume Or decreasing the volume of a container that has been sealed from contact with the outside Negative pressure: Produced by: Removing air particles from a fixed volume Or increasing the volume of a container sealed from contact with the outside

Quiet vs. forced inspiration Quiet inspiration: Inhalation of air during periods of rest. Primarily diaphragmatic action. Forced inspiration: Inhalation of air during periods of physical activity (including singing & preparing to speak). Utilizes diaphragm and external intercostals, as well as accessory muscles.

Passive vs. Active expiration Passive expiration: Relaxing of muscles used for inspiration driven by torque, elasticity, and gravity Active expiration: Thoracic contraction forces air out of the lungs beyond that which is expired in passive expiration

Torque, elasticity, and gravity Quiet vs. forced inspiration Active vs. passive expiration

Torque, elasticity, and gravity twisting of a shaft (or in this case a rib) while not permitting one end to move. Elasticity: The force associated with maintaining an object’s shape – a restoring force Gravity: Pulls abdominal viscera downward and pulls rib cage down to resting positioning. 3 forces always present acting on the diaphragm. Any time you add force that can be twisted will drive that object back to its original shape.

Volumes vs. Capacities Air volume: Capacity: Respiratory cycle Quantity of air held in the lungs. Measured in liter (L), mililiters (ml), or cubic centimeters (cc). Capacity: Functional units. Refer to combinations of volumes that express physiological limits. Same units as volume Respiratory cycle One complete inspiration and expiration Volume of space in the lungs

Volumes and Capacities Normative data: Males vs. females Males greater volumes, and thus capacities. Volumes peak between 20-30 years and then steadily decline VC a function of body, age, weight, and height.

Pressures of the Respiratory System

Pressure Atmospheric pressure: Intrapleural pressure: Pressure outside the body. Intrapleural pressure: Pressure in the space between parietal and visceral pleurae of the thoracic cavity. Alveolar pressure: Pressure within alveoli. Intraoral pressure: Pressure within the mouth. Subglottal pressure: Pressure below the vocal folds.

Pressure-Quiet respiration The interaction of these pressures and muscle contraction are responsible for respiration. Contraction of diaphragm decreases intrapleural pressure Lungs expand, dropping alveolar pressure. Relax diaphragm, intrapleural pressure increases. Alveolar pressure increases and air leaves lungs.

Pressures of the Respiratory Tissues During inspiration muscle activity overcomes forces of torque, elasticity, and gravity. Inspiration is an active process. During exhalation, passive forces of torque, elasticity, and gravity are utilized.

Pressures of the Respiratory Tissues The more an elastic matter is distorted, the greater the forces of restoration that drive that matter back to its resting position The greater the amount of thoracic expansion, the more forcefully it will be driven back to resting (relaxation) volume and the more difficult it will be to hold in its expanded state

Relaxation Pressure Curve Tidal Volume

Relaxation Pressure Curve 38% of vital capacity represents equilibrium or zero pressure. Recoil pressures of tissues allow for expiration of ~ 55% VC. After 55% VC, muscle of expiration are more active.

Pressures and Muscle Activity of Speech

Pressures of Speech Subglottal pressure Maintaining pressure Minimal speech pressure 3-5 cm H2O Conversational speech pressure: 7 cm H2O Syllable stress Maintaining pressure Inhalation Speech vs. Quiet inhalation Exhalation Speech vs. Quiet expiration

Speech pressure curve

Muscle Activity during Speech Controlling speech pressure: Checking action: Activation of the muscles of inspiration and abdominal positioning during expiration to control flow of air. Inspiration Diaphragm and external internal intercostals and preparatory abdominal activity Expiration Internal intercostals, External obliques, rectus abdominis, & latissimus dorsi

Review

Review Torque, elasticity, and gravity Volumes and capacities volumes make up capacities Pressures Atmospheric Alveolar Intrapleural Muscle activity during speech Checking action

Respiration and the Thorax The Rib-Lung “Battle” The ribs are curved bones that are under substantial force to “straighten out” Therefore, they are in a sense pulling the thorax apart, or expanding it laterally The lungs are under significant pressure to shrink In cadavers, the lungs often tear themselves away from the lining of the thorax, and shrink like a dried sponge Therefore, they are, in a sense, pulling the thorax toward the midline The lungs and ribs, then, establish a state of equilibrium, or a baseline size for the thoracic cavity from which an individual will make various manipulations

Respiration and the Thorax Inspiration, or inhalation Musculature Diaphragm receives innervation to contract from the medulla, which is the lower brainstem Pulls downward, which enlarges the thoracic space Simultaneously, the intercostal muscles are stimulated Two sets of intercostal muscles or “inter-rib” muscles External intercostals – connect the osseous portions of the ribs across the outsider (lateral) surface Internal intercostals – connect osseous portion of ribs to cartilaginous portion, near sternum - Two sets of internal intercostals Interchondral portion – connects the cartilaginous portion of ribs Interosseus portion – connects the bony portion of the ribs

Active/Passive Breathing

Respiration and the Thorax Inspiration, or inhalation: Muscle action Diaphragm lowers when it contracts, analogous to lowering the floor of the barrel Intercostal muscles contract The external intercostals raise the ribcage The interchondral portion of the internal interchondrals twist the ribs up and out Additional muscles, the scalenes, and sternocleidomastoid also elevate the ribcage The cumulative action, then is one in which the ribs are elevated, and twisted outward, thereby enlarging the thoracic cavity

Respiration and the Thorax Speech Breathing – Considerations regarding lung/thorax volume A far larger inspiration is required for active breathing The expiration phase consists of two portions Initiallly, the passive contraction of the thorax is slowed by the muscles of inspiration After the relaxation volume is reached, if the speaker wishes to continue, additional thoracic contraction must be carried out The passive forces of expiration, then, provide a “background force” that diminishes as the thorax approaches, then reaches its relaxation volume Active Expiration is continued through the contraction of muscles that raise the diaphragm, and further lower the ribcage

Respiration and the Thorax Speech breathing – distinct from quiet respiration because the expiration phase takes on far greater importance, and requires far more time Inspiration phase is often exaggerated by increased contraction of rib elevators The release of air is regulated and slowed relative to the passive expiration of quiet breathing

Respiration and the Thorax Speech Breathing: Regulating the expiration Contraction of the muscles of inspiration slows the passive expiration Slowing the passive expiration provides the talker the opportunity to shape the expiration into speech sounds During quiet respiration, 40% of the respiratory cycle is inspiration, 60% expiration During active, or speech breathing, the proportions change to 90-10 favoring expiration

Respiration and the Thorax Speech Breathing – Considerations regarding lung/thorax volume Tidal Volume – the amount of air exchanged in a typical, quiet respiration cycle - About 0.5 liters Vital Capacity – the maximum amount of air that can be exchanged in a person’s respiration cycle - About 5 liters Total lung capacity includes about another 2 liters (the residual volume) that is typically not expelled Therefore tidal volume is about 10% of the vital capacity The amount of air in the lungs when the V. folds are open and the pressure is equal with the atmosphere is the relaxation volume

Respiration and the Thorax

Respiration and the Thorax Speech Breathing – Considerations regarding lung/thorax volume A far larger inspiration is required for active breathing The expiration phase consists of two portions Initiallly, the passive contraction of the thorax is slowed by the muscles of inspiration After the relaxation volume is reached, if the speaker wishes to continue, additional thoracic contraction must be carried out The passive forces of expiration, then, provide a “background force” that diminishes as the thorax approaches, then reaches its relaxation volume Active Expiration is continued through the contraction of muscles that raise the diaphragm, and further lower the ribcage

Respiration and the Thorax Speech Breathing – Expiration phase Contraction of abdominal muscles Pushes abdominal viscera toward the backbone Squeezes the fluids/tissues upward (can’t go inferiorly (pelvis), or posteriorly (vertebral column) Elevates the diaphragm (raises the floor of the thorax) Contraction of the interosseous portion of the internal interchondrals Pulls the ribs closer together and down Overall action of speech expiration is to produce a gradual release of sub-glottal air pressure The rate at which the pressure is expelled is held constant through the muscle control outlined above

Respiration and the Thorax Speech Breathing – Expiration phase Correlation between the power of speech and the rate of expiration Intense speech requires a more powerful expelling of air Therefore the air is used up more quickly, and loud speech cannot be sustained as long as normal speech The pressure level is sustained, as in normal speech, but at a higher level

Respiration and the Thorax Differences between loud and normal speech About 25% of the vital capacity is used for normal speech Loud speech requires far more subglottal pressure, therefore more air to sustain the speech – estimates place the amount at about 40% of the vital capacity Additional strain is then placed on the valving mechanism (the vocal folds) when loud speech is generated

Respiration and the Thorax

Respiration and the Thorax Voice disorders May be due to problems with respiration in cases where insufficient subglottal air pressure is generated May also result from difficulty coordinating the muscles of respiration Such difficulty would reduce the effectiveness of the power source for speech For example, talker may not raise the ribcage in synchrony with the lowering of the diaphragm