Interval Ratio Research Articles

Sleep apnea-associated hypertension and reversible left ventricular hypertrophy

Children with sleep apnea syndrome may have persistent marked elevation of systemic blood pressure, 1,2 which is potentially reversible in adolescents 3 and adults 4' s when the underlying apnea is effectively treated. The occurrence and potential reversibility of marked left ventricular hypertrophy associated with this secondary form of hypertension has not, to our knowledge, been previously reported: We report two siblings with significant hemodynamic complications of this syndrome. CASE REPORTS Patient 1. This black male patient was first seen at age 2 years because of severe respiratory distress after a 5-day history of cough and congestion. In the emergency room, he was unresponsive, with perioral cyanosis and poor air exchange. His weight (22.7 kg) was >95th percentile for age, and height was 86 cm (30th percentile for age). His initial blood pressure was 155/78 (>90th percentile for age and sex), but increased to a maximum of 200/130 within 12 hours. This was controlled initially with nitroprusside intravenously, then captopril and chlorothiazide orally. During this hospitalization, he required prolonged ventiiatory support, bronchodilati0n, and therapy for hypertension and heart failure. The chest radiograph showed cardiomegaly, and M-mode echocardiogram showed a large left ventricular diameter (4.2 cm), increased mass (49 g), and elevated right (0.52) and left (0.44) ventricular systolic time interval ratios. Measurements of the left ventricular posterior wall (0.6 cm) and septum (0.6 cm) were slightly increased for age and height. 6 A morning serum cortisol concentration was normal, as were results of thyroid function studies, serum lipid values, and bone age. He was eventually discharged with a diagnosis of severe bronchospasm leading to respiratory failure and congestive heart failure. For blood pressure control, captopril and chlorothiazide were pr escribed, with a 1200-calorie diet and sodium intake restriction. With this regimen, serial blood pressure measurements were normal (106/60 supine) for age and sex. Other medications included metaproterenol and phenobarbital.

Attenuation and ratio—National standards

In national standards laboratories, the popular attenuation measurement techniques are: RF, IF, vector IF, and AF substitution; power ratio, voltage ratio, time-interval ratio, and six-port methods; and a procedure that employs a Josephson junction in a superconducting ring. These nine techniques are briefly described, the dynamic ranges and accuracies achieved with them are reported, and their relative merits are discussed. The later sections are devoted to: attenuation measurement techniques used in industry and elsewhere, voltage doubling circuits, attenuation traveling standards, errors and uncertainties associated with attenuation measurements, and international attenuation comparisons. An analysis of the results obtained in four recent international comparisons is included.

Microwave Attenuation Measurement by Time-Interval Ratio

A new method of measuring microwave attenuation using time or frequency as the reference is described. It is a power ratio type of system in which power flowing through the unknown attenuator is controlled by a constant pulsewidth, variable period, and pulse-modulated p-i-n diode switch. This power is detected by a thin-film thermocouple (TFT), the output of which is compared with that of a similar reference thermocouple whose input is a small constant fraction of the source power. The duty cycle required for equal thermocouple outputs is simply related to the unknown attenuation. The method is independent of detector linearity, and when compared with precise measurement standards, the system was found to be capable of measuring attenuation of up to at least 20 dB with an accuracy of ±0.001 dB/10 dB.

Early cardiac changes related to radiation therapy

To investigate the incidence and severity of possible radiation-induced cardiac changes, 21 women without heart disease were investigated serially by echocardiography and by measuring systolic time intervals before and up to 6 months after postoperative radiation therapy because of breast cancer. Radiation was associated with a decrease in fractional systolic shortening of the left ventricular (LV) minor-axis diameter, from 0.35 ± 0.05 to 0.32 ± 0.06 (p < 0.005), and in the systolic blood pressure/end-systolic diameter ratio, from 4.4 ± 1.2 to 3.9 ± 0.9 mm Hg/mm (p < 0.005). The mitral E point-septal separation increased, from 2.8 ± 1.5 to 4.2 ± 2.5 mm (p < 0.005). The preejection period/LV ejection time ratio of systolic time intervals increased, but only the decrease within 6 months after therapy was significant (p < 0.005). All these changes reflect slight transient depression of LV function, which became normalized within 6 months after therapy. Up to 6 months after therapy, a slight pericardial effusion was found in 33% of the patients. Hence, conventional radiation therapy appeared to cause an acute transient and usually symptomless decrease in LV function, and later, slight pericardial effusion in one-third of the patients.

Hearing Loss and Persistent Pulmonary Hypertension-Reply

In Reply .—Dr Horgan has made several important observations regarding our report. We did not address mortality rate in our study nor did we intend to suggest that it was 0%; that information was neither available nor retrievable retrospectively. It is now possible to define PFC (PPHN) with greater accuracy than was available to us, particularly during the early study period. As Dr Horgan notes, Fox and Duara 1 suggested one or more of the following as diagnostic tests for PPHN, although it is not clear which one(s) is(are) considered diagnostic: (1) hyperoxia test (term infants only); (2) preductal and postductal arterial oxygen levels; (3) hyperoxia-hyperventilation test; and (4) echocardiographic evaluation of systolic time interval ratios and/or myocardial function. In our study the diagnosis was made by the attending neonatologist from a combination of clinical factors as well as echocardiographic findings in some patients. The four patients who received oxygen

Long-term echocardiographic evaluation of cardiac size and function in patients with Kawasaki disease

The long-term effects of Kawasaki disease on the cardiac function were evaluated in 67 patients. Serial M-mode echocardiograms were obtained at the time of the initial diagnosis, 1 to 3 months, at 3 to 12 months, and at > 12 months following the diagnosis. Left ventricular and left atrial dimensions, shortening fraction, left and right ventricular systolic time interval ratios, and computer analysis of digitized echoes of the left ventricular chamber and posterior wall were obtained. The left atrial and left ventricular dimensions were abnormal in half of the patients throughout the study periods. The shortening fraction was abnormal initially but became normal by the end of 3 months. The peak rates of emptying of the left ventricle and thickening of the posterior wall were significantly reduced in all evaluation periods. In addition, the peak rate of diastolic thinning of the posterior wall was reduced, although the peak rate of filling remained normal. Finally, more than 30% of patients studied beyond 12 months had a prolonged major filling and thinning period. There was no difference between patients with or without coronary artery aneurysms. All other systolic and diastolic phase intervals and rates of changes were normal. Contrary to previously published reports, we conclude that patients with Kawasaki disease who do not have demonstrable coronary artery disease, exhibit abnormalities of cardiac chamber size and function long after their acute illness.

Relationship of prospective diabetes control in pregnancy to neonatal cardiorespiratory function

We evaluated two groups of diabetic women in pregnancy who differed primarily in the time of initiation of careful diabetes management. Group A (early) were entered in the first trimester (n = 35); group B (late) were entered in the late second or early third trimester (n = 28). Normal women delivering at the same period were used as controls (n = 23). All infants were evaluated by a thorough clinical and echocardiographic examination between 24 and 72 hours of life. Both groups of infants of diabetic mothers had mild increase in mean thickness of ventricular and septal walls compared with those of normal newborn infants, and both had a significant percentage with septal hypertrophy (43% vs 39%). None of the infants in the early group had respiratory symptoms requiring oxygen therapy, compared with 19% in the late group. The early group had significantly fewer infants with elevated right ventricular systolic time interval ratios than did the late group (20% vs 50%); none of the normal infants had elevated ratios. We conclude that careful management of diabetes in pregnancy reduces the severity of hypertrophic cardiomyopathy, although no advantage of early vs late management was obvious. Early management does significantly reduce the number of infants of diabetic mothers who develop respiratory symptoms requiring oxygen therapy.

Cardiac size and function in children with sickle cell anemia

Cardiac size and function were studied echocardiographically in 124 children with sickle cell anemia. A group of 78 healthy black children served as control subjects. Sickle cell patients exhibited progressive chamber enlargement and progressively increasing left ventricular mass. Although contractility indices were normal, when the opposing influences of volume overload due to anemia and ventricular dysfunction were separated, abnormalities of systolic time intervals were identified. Left ventricular systolic time interval ratio and left ventricular preejection period were higher in the sickle cell group and became increasingly abnormal with growth, suggesting that left ventricular function deteriorated with time.

CARDIAC DYSFUNCTION IN HEMOLYTIC UREMIC SYNDROME (HUS)

In HUS, myocardial involvement is infrequent and attributed to metabolic complications of acute renal failure or anemia. To better define the incidence of cardiac dysfunction, we studied ECG and Echo-cardiograms(ECHO) in 12 children(6M, 6F;ages1½-9yr) with HUS which was mild(1), moderately severe(7) or severe(4). At the time of studies, all pts were stable [peritoneal dialysis (11), diuresis(1)] with normal serum chemistry and acid base status. Average Hgb was>8g/dl. 2/12 had mild hypertension. The studies were repeated in 48hr(3), lmo(2), 8mo(1), 18mo(1). SGOT levels were elevated in 6/6. 5/12 showed ECHO evidence of myocardial dysfunction e.g: increase in left atrial and ventricular (LV) size, reduction in LV shortening and ejection fractions and prolongation of LV systolic time interval ratio. Except LV size, all ECHO changes improved minimally at 48hr but markedly at 1mo, were normal at 8mo(1). Persistent LV thickness at 18mo was associated with hypertension and renal insufficiency(1). There were 5 abnormal ECGs-persistent sinus tachycardia(4), decreased voltage (2), LV hypertrophy(2), ST segment depression(2), T wave inversion(1). 4/5 abnormal studies were in children with severe and 1 in moderately severe HUS. of 5 HUS pts with cardiac dysfunction, 2 recovered, 2 developed hypertension and renal failure, 1 died, while 6/7 pts without cardiac dysfunction recovered & 1 died. Conclusions: Cardiac dysfunction(1) occurs in 40% of HUS, 2) is associated with severe HUS 3) cannot be accounted by metabolic derangements or anemia.

Harmonic generation mechanism in organ pipes.

A whole view on the harmonic generation in organ pipes is presented. It consists ofelementary processes:(a) excitory source spectrum generation by the jet, (b) filtrationby the inharmonic normal modes of the passive system, and (c) radiation from the pipeends. Lateral jet velocity distribution is responsible for the source spectrum. Filtrationand radiation emphasize the resultant source spectrum. Harmonic generationmechanism is classified into the unsaturated and saturatea regimes, and formulated onthe basis of current-and pressure-drive models. Theoretical consideration deduced:(1) Contribution of the pressure-drive to the harmonic generation is not significant.(2) Harmonic structure and its development in the unsaturated regime are defined bythe matrix of the jet offset and the vector of the jet deflection amplitude.(3) A decisivefactor determining the harmonic structure in the fully saturated regime is the time interval ratio of the jet switching action.

Echocardiographic Characteristics of Premature Infants with Patent Ductus Arteriosus

As part of a multicenter collaborative study, M-mode echocardiograms were obtained shortly after birth on 3,559 premature infants with birth weight ≤1,750 g. Of these infants, 1,496 did not develop a cardiac murmur or other signs of a "hemodynamically significant" patent ductus arteriosus (PDA). Echocardiographic parameters from this "normal" group were compared with results obtained from 415 infants in whom PDA was diagnosed on the basis of clinical findings alone, irrespective of the echocardiogram (PDA group). The best discrimination between the two groups, when considering a single parameter, was provided by a left atrial to aortic root ratio (LA/AO) of 1.40, a left ventricular to aortic root ratio (LV/AO) of 2.10, or a left ventricular systolic time interval ratio (LPEP/LVET) of 0.27. Multivariate analysis demonstrated that better separation between the two groups occurred when the left atrial to aortic root ratio and the left ventricular systolic time interval ratio were considered jointly. Because of a large degree of overlap of all echocardiographic variables between the normal group and the group with PDA, the echocardiogram alone was not a good indicator of PDA. However, when used in conjunction with a priori estimates of the probability of PDA (based, for example, on birth weight and degree of respiratory disease), use of echocardiographic data was found to improve the detection of hemodynamically significant patent ductus arteriosus in premature infants.

Left ventricular dysfunction in Rocky Mountain spotted fever.

Rocky Mountain spotted fever is a serious infectious disease that continues to occur with increasing incidence in various areas of the United States. A high case-fatality ratio (11%) persists in spite of availability of adequate chemotherapeutic agents, and the cardiac involvement may play an important role in the final outcome of some cases. To assess the effect of the disease on left ventricular function 13 patients underwent M-mode echocardiographic examination on admission to a children's hospital. Increased left ventricular dimension was found in 3 patients and decreased left ventricular shortening fraction in 9. Diminished mean velocity of circumferential fiber shortening and increased left ventricular systolic time interval ratios were found in 8 patients and increased mitral valve E point to ventricular septal separation in 9. One patient died and biventricular dilatation with diffuse myocarditis was seen at autopsy. Repeat echo examination was available in 11 patients at follow-up (mean 5 months). Abnormal E mitral point to ventricular septal separation remained in 4 patients and decreased left ventricular shortening fraction in 2. The long-term prognosis for this group is unknown. Myocardial involvement is frequently present in Rocky Mountain spotted fever; close monitoring and aggressive therapeutic approach are essential if the high case-fatality ratio is to be reduced.

Rapid Pituitary and Peripheral Tissue Responses to Intravenous L-Triiodothyronine in Hypothyroidism*

Acute cardiovascular, renal, pulmonary, metabolic, and pituitary responses to therapy of hypothyroidism with 25 micrograms iv T3 (group I G-I, n = 11) or 50 micrograms iv T3 (group II, G-II, n = 10)/day for 1 week have been studied. Serum T3 levels were acutely normalized in both groups with the mean basal serum T3 levels (X +/- SE) after 7 days, 98 +/- 10 micrograms/dl and 229 +/- 19 ng/dl, respectively. Myocardial performance, noninvasively assessed by the pulse wave arrival time (QKd) and the phonocardiographic systolic time interval ratio was significantly altered after 1 day of therapy (QKd for G-I = -10 +/- 4 msec, P less than 0.05; and for G-II = -18 +/- 14 msec, P less than 0.01). After 7 treatment days, both the mean QKd (203 +/- 7 msec, P less than 0.001) and phonocardiographic systolic time interval ratio (0.41 +/- 0.02, P less than 0.01) were within the normal range in G-II. Abnormal pretreatment renal excretion of an oral water load (G-I, 65 +/- 6%; and G-II, 57 +/- 6%) was also reversed after 1 week (G-I, 84 +/- 5%, P less than 0.05; and G-II, 89 +/- 5%, P less than 0.01). Patients with blunted hypercapnic (n = 6) and hypoxic (n = 4) ventilatory drives were improved in both groups after 6 days. The mean basal metabolic rate, serum cholesterol, and serum creatine phosphokinase were altered by the week of therapy in a dose-response manner, and were in the normal range in G-II. Pituitary TSH secretion was promptly suppressed in both groups. Two hours after the first T3 dose, the mean serum TSH for G-I and G-II decreased to 85% (P less than 0.02) and 70% (P less than 0.001) of their respective pretreatment values. After 7 days of therapy, the mean basal TSH levels had declined to 75% (P less than 0.001) and 5% (P less than 0.001%) of pretreatment, respectively. In comparison with previous observations of responses to 100 micrograms/day iv T4 for 1 week, the 25 micrograms dose T3 was equivalent in terms of changes in basal serum T3 and peripheral (nonpituitary) tissue responses, but less effective than T4 in lowering serum TSH. Based on these parameters, 50 micrograms/day iv T3 was the most effective of the three regimens within this time frame. The implications of these observations in the clinical management of severe complicated myxedema are discussed.

Long-term follow-up study after closure of secundum atrial septal defect in children: An echocardiographic study

Serial echocardiography was performed in 51 children with isolated secundum atrial septal defect before and after surgery to measure the effects of chronic right ventricular overload on ventricular function. Right ventricular dilation increased dramatically with growth and with size of the left to right shunt only in the youngest children (body surface area less than 0.5 m 2). A lesser effect of growth and no significant effect of shunt size were noted in older children. Although an initial decrease in right ventricular size occurred in the first 3 months after operation, persistent right ventricular dilation remained up to 5 years after closure of the interatrial defect in more than 80 percent of patients. Preoperatively, the ratio of the right ventricular preelection period to ejection time was significantly less than that of normal children. This ratio increased dramatically after operation, exceeding normal values early in the postoperative period in 18 of 48 children and persisting in 6 of 22 after 3 months. Left ventricular dimensions were normal early and late after operation. Left ventricular function was apparently normal, although] an exceptionally high shortening fraction was noted in 22 (44 percent) of 51 children after operation. Aortic systolic time interval ratios decreased after operation from high normal to low normal values. It is hypothesized that the persistent enlargement of the right ventricle after operation may be due to the chronic preoperative dilation secondary to chronic interatrial shunting. The abnormally high shortening fraction after operation may result from an abnormal left ventricular geometric configuration or abnormality of filling. It is suggested that surgical closure of the atrial defect in the first 3 years of life may prevent these abnormalities.

Echocardiographic changes of cardiac structures and LV function in newborns

Cardiac chamber size and function indices were studied repeatedly over the first months of life in two groups of babies, born either spontaneously or by caesarian section under peridural anaesthesia. For cardiac chamber size, no significant differences were found between the two groups: cardiac structures increased in size as a linear function of age and weight in all babies. Right ventricular systolic time interval ratios, however, were higher at birth in babies born by caesarian section, and dropped more rapidly during the first 24h. The decrease of RV systolic time interval ratios followed a parabolic function for both groups, thus reflecting the physiological decrease of pulmonary vascular resistance after birth. The possible causes of more rapid decrease in pulmonary vascular resistance in babies born by caesarian section is discussed.

Utility of M-Mode Echocardiography for Early Identification of Infants with Persistent Pulmonary Hypertension of the Newborn

The clinical syndrome of persistent pulmonary hypertension of the newborn (PPHN) still carries high mortality in spite of improved neonatal care. The purpose of this prospective study was to assess the utility of M-mode echocardiography for the early identification of infants with PPHN prior to clinical deterioration. Echocardiograms of 51 infants who needed fractional inspiratory oxygen (FIO2) greater than or equal to 0.25 to maintain adequate PaO2 within 36 hours of life were compared to those of 115 healthy full-term and preterm newborns. Of the 51 infants, ten had elevated systolic time interval ratios of both ventricles simultaneously (ventricular pre-ejection period to ventricular ejection time [RPEP/RVET greater than or equal to 0.50, LPEP/LVET greater than 0.38]). All of these newborns had PPHN that was manifest clinically by 11 to 30 hours of age. The echocardiographic findings preceded clinical deterioration by at least one to five hours in all cases. The other 41 infants had clinical courses consistent with uncomplicated pulmonary disease. These data indicate that systolic time interval ratios, although not accurate measures of pulmonary arterial pressure and/or pulmonary vascular resistance, permit early identification of infants with PPHN and separation from others with uncomplicated pulmonary disease.

1283 RIGHT VENTRICULAR DYSFUNCTION IN PREMATURE INFANTS

The purpose of this study was to determine the relationship of pulmonary systolic time interval ratios (PSTI) to ductal shunting (DS) in premature infants. Echocardiograms were obtained on 102 infants (Wt <2.4 Kg) at 1-28 days of age (mean 5.6) because of symptomatic DS. They were divided into 2 groups based on PSTI (Group I<.35, n=57; Group II> .35, n=45). They were compared for age, weight, surface area, chamber dimensions, aortic root size, left ventricular time intervals and contractility. No significant differences were found except that Group II infants were younger. Echocardiographic left heart volume overload was found in 40/57 (70%) of Group I and 33/45 (73%) of Group II infants. No differences in the incidence of DS, chamber size or left ventricular function were seen with elevated PSTI's. Elevated pulmonary vascular resistance was expected to reduce DS. The lack of an effect of high PSTI's on DS suggests that the high PSTI's were not reflecting increased pulmonary resistance. Elevated PSTI's in premature infants with a patent ductus arteriosus are likely to be due to right ventricular dysfunction from coronary insufficiency or hypoxia.

Normal Pulmonary Vascular Resistance and Left Ventricular Hypertrophy in Young Infants with Bronchopulmonary Dysplasia: An Echocardiographic and Pathologic Study

To evaluate the cardiac anatomy and functional hemodynamics in young infants with chronic lung disease, nine patients, aged 2 to 7 months, with a clinical diagnosis of bronchopulmonary dysplasia (BPD) underwent echocardiographic examination. All infants required supplemental O2 (mean FIO2 35%) to maintain adequate systemic oxygenation (Pao2 greater than 50 mm Hg). None of the infants had evidence of a patent ductus arteriosus at the time of examination. Echocardiographic measurements of left and right ventricular systolic time intervals revealed normal systolic time interval ratios suggesting pulmonary vascular resistances. However, echocardiographic evidence of left ventricular hypertrophy was found in eight of the nine infants, while right ventricular anterior wall thickness and right ventricular diastolic dimensions were not increased. Two infants died; marked left ventricular hypertrophy was noted at the time of postmortem examination while the right ventricular wall thickness was normal. The findings of left ventricular hypertrophy led to a retrospective review of autopsy material of seven patients who died with BPD over the past year. In six of seven cases examined, left ventricular posterior wall thickening was noted (range 7 to 11 mm); while the right ventricular wall thickness was normal (range 2 to 5 mm). These data suggest that (1) as assessed by echocardiography, the pulmonary vascular resistance is not significantly elevated in young infants with BPD, and (2) a hypertrophic left ventricle evolves which may assume importance in the pathogenesis of pulmonary edema in BPD, though the precise etiology remains undetermined.

Perioperative echocardiographic evaluation of cardiovascular function: assessment of changing hemodynamic state.

To evaluate echocardiographic assessment of ventricular function in a changing hemodynamic situation, 20 infants and children undergoing open heart surgery were examined preoperatively and 1,4 and 24 hours postoperatively by this technique. Clinical evaluation and measurements of cardiac output were obtained simultaneously with each echocardiogram. On the basis of their clinical course and cardiac output, the patients were divided into two groups: group 1 - cardiac index > 2.3 1/min/m2 without inotropic support (n = 9); and group 2 - cardiac index less than or equal to 2.3 1/min/m2 and/or need for inotropic support (n = 11). Of the echocardiographic measurements obtained, the left ventricular systolic time interval ratio (left ventricular preejection period/left ventricular ejection time ([LVPEP/LVET] correlated significantly with the clinical course, separating the two groups of patients completely at each determination. The aortic root velocity (AoV), a new index defined as the anterior excursion (in degrees) of the aortic root from the horizontal plane with systole, also correlated with the clinical course, although this was not statistically significant. Serial change in LVPEP/LVET and AoV crrrelated with changes in clinical status and cardiac output for individual patients. Using a formula based on the opening slope of the mitral valve, echocardiographic estimations of cardiac output correlated well with those determined by dye dilution. The results indicate that selected echocardiographic indexes can be used for serial assessment of cardiac performance in patients with a changing hemodynamic state.

Thallium-scan myocardial defects and echocardiographic abnormalities in patients with sarcoidosis without clinical cardiac dysfunction: An analysis of 44 patients

Sarcoidosis of the myocardium, an illness occurring predominantly in young adults, frequently becomes clinically apparent when the disease is far advanced. Since the thallium myocardial perfusion scan (TMPS) is known to be capable of detecting granulomas, it seemed to be promising as a noninvasive means of screening for this complication of sarcoidosis. We, therefore, examined 44 consecutive patients with sarcoidosis, none of whom had clinical evidence of heart disease, utilizing TMPS, echocardiography, electrocardiography, systolic time interval ratios (PEP:LVET) and 24-hour Holter monitoring. TMPS disclosed left ventricular defects in 14 patients (32 per cent) and abnormalities of the right ventricle in an additional four patients. Left ventricular abnormalities on the TMPS were associated with echocardiographic evidence of left ventricular dysfunction (widened mitral E point septal separation) but not with abnormalities on Holter monitoring or electrocardiograms. Systolic time interval ratios were insensitive but highly specific for the presence of abnormalities on the TMPS. We conclude that the TMPS frequently discloses abnormalities in sarcoidosis, which may be a reflection of its sensitivity in this setting.