- The arterial pressure usually raises and falls 4 to 6 mm Hg in a wave like manner causing “respiratory waves”. The probable mechanism of these waves has been proposed in the following statements:
A. The more negative intrathoracic pressure during inspiration reduces the quantity of blood returning to the left side of the heart causing decreased cardiac output.
B. The changes of intrathoracic pressure during respiration can excite vascular and atrial stretch
receptors which affect heart and blood vessels.
C. The activity of medullary respiratory centers can influence the vasomotor center.
D. The “respiratory waves” are outcome of the oscillation of the central nervous system ischemic pressure control mechanism.
Which of the above statement(s) is/are NOT appropriate?
(1) Only A (2) A and B
(3) B and C (4) Only D
The phenomenon of respiratory waves in arterial pressure refers to the slight rise and fall of arterial pressure by about 4 to 6 mm Hg synchronized with breathing. These waves are important indicators of cardiovascular and respiratory interactions.
Evaluating the Proposed Statements
A. More negative intrathoracic pressure during inspiration reduces venous return to the left side of the heart, causing decreased cardiac output.
-
Correct. During inspiration, negative intrathoracic pressure increases venous return to the right heart but transiently reduces left ventricular filling and output, reflected as arterial pressure changes.
B. Changes in intrathoracic pressure during respiration can excite vascular and atrial stretch receptors, affecting heart and blood vessels.
-
Correct. Stretch receptors are sensitive to volume and pressure changes during respiratory cycles, contributing to reflex cardiovascular adjustments.
C. Activity of medullary respiratory centers can influence the vasomotor center.
-
Correct. Respiratory centers modulate autonomic centers including vasomotor neurons affecting vascular tone and blood pressure.
D. Respiratory waves are due to oscillations within CNS ischemic pressure control mechanisms.
-
Incorrect. Respiratory waves arise from mechanical and reflex cardiovascular-respiratory interactions, not ischemic CNS oscillations.
Which Statements Are NOT Appropriate?
Given A, B, and C are physiologically valid explanations for how respiratory waves occur, but D proposes an incorrect cause.
Therefore:
(4) Only D is NOT appropriate.
Physiological Explanation
-
During inspiration, the thorax expansion lowers intrathoracic pressure, altering venous return differently on the right and left sides.
-
This transient imbalance causes arterial pressure changes visible as respiratory waves.
-
Reflexes from stretch receptors and central autonomic modulation integrate respiratory and cardiovascular functions.
-
The CNS ischemic pressure control explanation is unsupported for this phenomenon.
Summary Table
Statement Correctness Explanation A Correct Negative intrathoracic pressure alters cardiac output B Correct Stretch receptors respond to respiratory pressure changes C Correct Respiratory centers influence vasomotor centers D Incorrect Respiratory waves are not caused by CNS ischemic oscillations
Conclusion
The correct answer identifying the statements NOT appropriate about respiratory waves is:
(4) Only D
-
2 Comments
Varsha Tatla
September 17, 2025Easy
Aakansha sharma Sharma
October 3, 2025(4) Only D