inspiration

(noun)

The drawing of air into the lungs, accomplished in mammals by elevation of the chest walls and flattening of the diaphragm.

Related Terms

Examples of inspiration in the following topics:

  • Inspiration

    • The pleural cavity normally has a lower pressure compared to ambient air (-3 mmHg normally and typically -6 mmHg during inspiration), so when it expands, the pressure inside the lungs drops.
    • The alveolar sacs themselves also expand as a result of being filled with air during inspiration, which contributes to the expansion inside the lung.
    • Eventually, the pressure inside the lung becomes less negative as the volume inside the lung increases, and when pressure and volume stabilize, the air movement stops, inspiration ends, and expiration (exhalation) will begin.
    • External intercostal muscles: muscles located in between the ribs that help the thoracic cavity (and thus pleural cavity) to expand during quiet and forced inspiration.
    • They provide a mechanism for inspiration when the diaphragm is injured and can't contract normally.

  • Neural Mechanisms (Respiratory Center)

    • The apneustic center sends signals for inspiration for long and deep breaths.
    • It controls the intensity of breathing and is inhibited by the stretch receptors of the pulmonary muscles at maximum depth of inspiration, or by signals from the pnuemotaxic center.
    • The pnuemotaxic center sends signals to inhibit inspiration that allows it to finely control the respiratory rate.

  • Proprioceptor Regulation of Breathing

    • While the volume of the lungs is proportional to the pressure of the pleural cavity as it expands and contracts during breathing, there is a risk of over-inflation of the lungs if inspiration becomes too deep for too long.
    • When the lungs are inflated to their maximum volume during inspiration, the pulmonary stretch receptors send an action potential signal to the medulla and pons in the brain through the vagus nerve.
    • As inspiration stops, expiration begins and the lung begins to deflate.
    • When this process is cyclical it is called a sinus arrhythmia, which is a generally normal physiological phenomenon in which there is short-term tachycardia during inspiration.

  • Heart Sounds

    • During inspiration (breathing in) there is slightly increased blood return to the right side of the heart, which causes the pulmonary valve to stay open slightly longer than the aortic valve.
    • The time between A2 and P2 is variable depending on the respiratory rate, but the split is generally only prominent in children during inspiration.

  • Heart Murmurs

    • Therefore, right-sided murmurs generally increase in intensity with inspiration.
    • This causes left-sided murmurs to generally decrease in intensity during inspiration.
    • Positive Carvallo's sign describes the increase in intensity of a tricuspid regurgitation murmur with inspiration.

  • Expiration

    • Expiration is typically a passive process that happens from the relaxation of the diaphragm muscle (that contracted during inspiration).
    • Note that these are not the same as the external intercostal muscles involved in inspiration.

  • Pericarditis

    • Substernal or left precordial pleuritic chest pain with radiation to the trapezius ridge (the bottom portion of scapula on the back), which is relieved by sitting up and bending forward and worsened by lying down (recumbent or supine position) or inspiration (taking a breath in), is the characteristic pain of pericarditis.
    • This can be seen in patients who are experiencing the classic signs of pericarditis but then show signs of relief, and progress to show signs of cardiac tamponade which include decreased alertness and lethargy, pulsus paradoxus (decrease of at least 10 mmHg of the systolic blood pressure upon inspiration), hypotension (due to decreased cardiac index), JVD (jugular vein distention from right sided heart failure and fluid overload), distant heart sounds on auscultation, and equilibration of all the diastolic blood pressures on cardiac catheterization due to the constriction of the pericardium by the fluid.

  • Pons

    • Within the pons is the pneumotaxic center, a nucleus in the pons that regulates the change from inspiration to expiration.

  • Pneumonia

    • Rales (or crackles) may be heard over the affected area during inspiration.

  • Intubation During Anesthesia

    • Specifically, intubation is considered if the arterial partial pressure of oxygen (PaO2) is less than 60 millimeters of mercury (mm Hg) while breathing an inspired O2 concentration (FIO2) of 50% or greater.