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Nghiệm pháp Valsalva

 Nghiệm pháp Valsalva như sau: ngậm miệng, bịt mũi, bịt tai, hít vào sâu rồi ép hơi thở ra thật mạnh (nhưng không cho hơi ra

Làm nghiệm pháp Valsalva như sau: ngậm miệng, bịt mũi, bịt tai, hít vào sâu rồi ép hơi thở ra thật mạnh (nhưng không cho hơi ra),

      I.                   CK Tai: tắc tai vòi Eustachian tubes.

II.                CK Niệu: Giãn tĩnh mạch thừng tinh (varicocele).

III.             CK Bụng: 1. thoát vị bẹn, 2. Trĩ.

IV.              CK Tim mạch: 1. Giảm trong: a. hẹp valve Đmc, b. hẹp đmphổi, c. Hở 3 lá. 2. Tăng trong: a. Bệnh cơ tim phì đại, b. Sa valve 2 lá.

V.                 Nội tk: để chẩn đoán tổn thương đốt sống cổ.

VI.              Mắt: xem chảy máu trước võng mạc khi bn ho, rặn đi cầu.

The Valsalva maneuver is performed by forcibly exhaling against a closed airway. Variations of the maneuver can be used either in medicine, as a test of cardiac function and autonomic nervous controlof the heart or to "clear" the ears and sinuses (equalize pressure) when ambient pressure changes, as in diving or aviation.

  1. Initial pressure rise: On application of expiratory force, pressure rises inside the chest forcing blood out of the pulmonary circulation into the left atrium. This causes a mild rise in blood pressure.
  2. Reduced venous return and compensation: Return of systemic blood to the heart is impeded by the pressure inside the chest. The output of the heart is reduced and blood pressure falls. This occurs from 5 to about 14 seconds in the illustration. The fall in blood pressure reflexively causes blood vessels to constrict with some rise in pressure (15 to 20 seconds). This compensation can be quite marked with pressure returning to near or even above normal, but the cardiac output and blood flow to the body remains low. During this time the pulse rate increases.
  3. Pressure release: The pressure on the chest is released, allowing the pulmonary vessels and the aorta to re-expand causing a further initial slight fall in pressure (20 to 23 seconds) due to decreased left ventricular return and increased aortic volume, respectively. Venous blood can once more enter the chest and the heart, cardiac output begins to increase.
  4. Return of cardiac output: Blood return to the heart is enhanced by the effect of entry of blood which had been dammed back, causing a rapid increase in cardiac output and of blood pressure (24 seconds on). The pressure usually rises above normal before returning to a normal level. With return of blood pressure, the pulse rate returns towards normal.

The Valsalva maneuver may be used to arrest episodes of supraventricular tachycardia. The maneuver can sometimes be used to diagnose heart abnormalities, especially when used in conjunction with echocardiogram. For example, the Valsalva maneuver classically increases the intensity of hypertrophic cardiomyopathy murmurs, viz. those of dynamic subvalvular left ventricular outflow obstruction; whereas it decreases the intensity of all other murmurs, including aortic stenosis and atrial septal defect.

The Valsalva maneuver alters heart rate through parasympathetic stimulation (i.e. the Vagus Nerve/ Cranial Nerve X). Vagal neuro-muscular junctions at the sinoatrial node release the neurotransmitteracetylcholine (ACh). Ligand-receptor binding causes several effects:1. ACh lowers the permiability of muscle cell membranes to sodium and calcium ions, resulting in a slower rate of pacemaker depolarization. Hence, the cell takes longer to generate an action potential.2. ACh also lowers the number of available L-type calcium channels, which elevates the cell’s threshold for action potentials. Thus, the cell needs to depolarize more than normal to fire an action potential.3. New research suggests that ACh also activates latent potassium channels in the cell membrane. Increased potassium ion influx decreases the maximum diastolic potential of the cell. That is, hyperpolarization decreases the membrane potential of the pacemaker cells.These effects elongate the time between pacemaker action potentials, which results in a slower heartbeat and a mechanism to interrupt or diagnosearrhythmia. In later phases of the valsalva maneuver (Phases II and III), heart rate elevates due tosympathetic interplay.  

 

Đăng bởi: ycantho - Ngày đăng: 21/10/2010
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