Posted by James
Although it has been evident that diseases of the lungs affect cardiovascular function, it has not been appreciated how simply and directly the lungs influence the heart because the heart is nestled between them in the chest. It rests on the parietal pleural surfaces of the cardiac indentations of the left and right lung, and on the diaphragm below. In front is the rigid sternum. Normally pleural pressures drop and volumes increase during inhalation while the reverse occurs during exhalation: during mechanical ventilation, pleural pressure and lung volume change in the same direction. At resting end-tidal lung volumes the heavy heart can sink deeply into the soft lung tissues in the supine or left and right lateral decubitus positions. However, at high lung volumes (such as at the total lung capacity normally selected for decubitus chest x-ray examination), the heart is held firmly by the relatively tense pleura and distended lung. It is almost incredible that cardiac function is still assessed solely in terms of rate, output, and intracardiac pressures (preload and afterload) without consideration of the pressures around the heart.
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Posted by James
The Problems
TJecently there have been considerable advances in our understanding of the role of the “hands that hold the heart” —the lungs which form the cardiac fossa in which the heart lies in the chest —in affecting cardiovascular function in health and in disease (Fig 1). I shall try to use this new knowledge to clarify some of the clinical problems of cardiopulmonary interactions that have puzzled physicians dealing with chest diseases.
Atrial Pressures
Is right or left ventricular failure caused by acute exacerbations of chronic obstructive pulmonary disease?
A raised jugular venous pressure occurs during exacerbations of obstructed airflow disease and has been regarded as a sign of right ventricular failure. It is more evident when there is a worsening of airflow obstruction attributable to a flare-up of respiratory infection. The possibility of right heart failure is often supported by the presence of a palpable liver and peripheral edema. However, these patients do not have heart failure by the usual criteria since they have a normal or increased cardiac output and are able to augment blood flow on exercise.
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Posted by James
Relationship of Doppler Velocity to Gradient
The Doppler peak left ventricular outflow tract velocity relates to the pressure gradient at the site of obstruction. If the Doppler signal is obtained nearly parallel to the flow of blood, this relationship is described by the modified Bernoulli equation: PG = 4 (V)2, where PG is the maximum instantaneous pressure gradient at the site of obstruction and V is the peak Doppler velocity. There is experimental and clinical evidence to support a good relationship of the Dopp- ler-derived peak gradient with that measured at manometry both at rest and following interventions in patients with HCM.
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Posted by James
Importance of Hemodynamic Subsets
Classification of patients with HCM according to the nature and severity of LVOTO may have important therapeutic and prognostic implications. Patients with resting LVOTO manifest the most severe and frequent symptoms as well as the most profound hemodynamic systolic and diastolic abnormalities. Untreated, this subset of patients has a poor prognosis, with one study reporting more than 50 percent to worsen symptomatically and 11 percent dying by four- year follow-up. For these reasons, aggressive therapy with Э-blockers, calcium antagonists, negative inotropic agents, and a lower threshold to performing septal myomectomy has been advised in this group of patients. Patients with nonobstructive HCM tend to have fewer symptoms, yet they may still demonstrate significant hemodynamic abnormalities related to the extent of left ventricular hypertrophy. Calcium antagonist therapy, which has primarily been advised in this group of patients, may provide symptomatic and hemodynamic improvement as well as result in regression of left ventricular hypertrophy 1610,17 patients with latent LVOTO are usually the least symptomatic, with fewer atrial and ventricular arrhythmias, normal left ventricular end-diastolic pressures, and normal diastolic filling characteristics. Thus, blockers are considered agents of choice in treating this hemodynamic subset. Negative inotropic agents are believed to be contraindicated.
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Posted by James
Baseline characteristics of all patient groups are indicated in Table 1. No differences in age were detected among the patient groups. More women than men were noted in the group with HCM than the group without HCM.
Echocardiography and Doppler parameters in the 15 normal subjects who underwent Amyl inhalation are shown in Table 2. No normal subject had resting systolic anterior movement of the mitral valve. Using 2 SD limits, normal Doppler peak resting left ventricular outflow tract velocity was established as ^2.1 m/s. The normal peak left ventricular outflow tract velocity after Amyl was established was ^2.7 m/s.
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Posted by James
Patient Population
Ail patients referred for Doppler echocardiographic evaluation of clinically suspected HCM during the period between January 1985 and June 1988 were enrolled. Baseline data, which were collected on 333 consecutive patients, included age, sex, and the reason for referral. Doppler echocardiograms were performed without changes in medications.
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Posted by James
“Datients with hypertrophic cardiomyopathy (HCM) may be categorized according to the presence and severity of left ventricular outflow tract obstruction (LVOTO). Such a classification identifies three hemodynamic subsets: absence of LVOTO, resting LVOTO, and latent or provocable LVOTO, all of which may have different therapeutic and prognostic significance. Continuous wave Doppler combined with 2-D and M-mode echocardiography offers a useful means by which to identify these hemodynamic subsets. Although inhalation of the vasodilator, amyl nitrite (Amyl), has long been recognized as a means to provoke latent LVOTO in patients with HCM, the value and safety of Amyl in patients undergoing ambulatory Doppler echocardiography has not been studied in a systematic fashion. Read the rest of this entry »