Wavelet transform to quantify heart rate variability and to assess its instantaneous changes

Heart rate variability is a recognized parameter for assessing autonomous nervous system activity. Fourier transform, the most commonly used method to analyze variability, does not offer an easy assessment of its dynamics because of limitations inherent in its stationary hypothesis. Conversely, wavelet transform allows analysis of nonstationary signals. We compared the respective yields of Fourier and wavelet transforms in analyzing heart rate variability during dynamic changes in autonomous nervous system balance induced by atropine and propranolol. Fourier and wavelet transforms were applied to sequences of heart rate intervals in six subjects receiving increasing doses of atropine and propranolol. At the lowest doses of atropine administered, heart rate variability increased, followed by a progressive decrease with higher doses. With the first dose of propranolol, there was a significant increase in heart rate variability, which progressively disappeared after the last dose. Wavelet transform gave significantly better quantitative analysis of heart rate variability than did Fourier transform during autonomous nervous system adaptations induced by both agents and provided novel temporally localized information.

Accuracy of an automatic and patient-triggered long-term solid memory ambulatory cardiac event recorder

This study evaluated the R-Test Evolution, a new type of cardiac event recorder bearing both patient-triggered and automatic capabilities. Its 7-day automatic arrhythmia analysis showed promising clinical advantages, especially when investigating patients with unexplained rare events such as syncope, feeling of weakness or faintness, palpitations, stroke, or in patients inconsistent in their use of patient-triggered recordings.

Accuracy of pulse oximetry during intense exercise under severe hypoxic conditions

There is a growing need to measure arterial oxygen saturation with a non-invasive method during heavy exercise under severe hypoxic conditions. Although the accuracy of pulse oximetry has been challenged by several authors, it has not been done under extreme conditions. The purpose of this study was to evaluate the accuracy of a pulse oximeter (Satllite. Datex, Finland) during exercise under hypoxic conditions where arterial oxygen saturation was below 75%, simulating exercise at extreme altitude. Ten healthy non-smoking men performed two exercise studies of 30 min under normoxia and under hypoxia on two consecutive days. The exercise intensity was 80% of maximal O2 consumption of VO2max. Arterial oxygen saturation measured by pulse oximetry was corrected (SpO2[corr]) according to previously published equations and was compared to arterial oxygen saturation (SaO2) in blood samples taken simultaneously from the radial artery. Reference arterial saturation values ranged from 57.2 to 97.6% for the whole data set. This data set was split according to low (SaO2 < or = 75%) and high (SaO2 > 75%) SaO2 values. The error of pulse oximetry (SpO2[corr]-SaO2) was 2.05 (0.87)% [mean (SD)] and 1.80 (1.81)% for high and low SaO2 values, respectively. SpO2[corr] and SaO2 were highly correlated (r = 0.93, SEE = 1.81) for low values. During high-intensity constant workload under severe hypoxic conditions, once corrected, pulse oximetry provides an estimate of SaO2 with a mean error of 2%. Thus, the correction previously described for SpO2 values above 75% saturation applies also to SpO2 values in the range of 57-75% during exercise under hypoxic conditions.

Maximal blood lactate level acts as a major discriminant variable in exercise testing for coronary artery disease detection in men

BACKGROUND

The interpretation of exercise stress testing for coronary artery disease detection is affected by the many differences in chosen variables and mathematical methods. We conducted a prospective trial to evaluate a global muscle fatigue parameter--the blood lactate level achieved at maximal exercise--as a method of distinguishing between diseased and nondiseased coronary status.

METHODS AND RESULTS

We evaluated 236 consecutive male patients without previous myocardial infarction who had been referred for the diagnosis of coronary artery disease. None of the patients had cardiomyopathy, severe cardiac heart failure, or valvular heart disease. Blood lactate concentration at maximal exercise was measured as well as other classic variables. Correlations between variables and coronary status as assessed by coronary arteriography were described using receiver operating characteristic (ROC) curves and logistic regression analysis. The first four most powerful variables (lactate level, maximal power output, exercise duration, and percentage of maximal predicted heart rate), which are directly representative of the global functional capacity, showed values of 0.777, 0.775, 0.760, and 0.740, respectively, by ROC curve analysis. Mean +/- SD blood lactate level at peak exercise reached 7.68 +/- 2.70 mmol/L in the 153 diseased and 10.56 +/- 2.75 mmol/L in the 83 nondiseased patients (P < .0001). After adjustment for other variables, blood lactate level remained a significant predictor of coronary artery disease by logistic regression analysis (adjusted odds ratio, 1.2; confidence interval, 1.04 to 1.4).

CONCLUSIONS

Global muscle fatigue as assessed by lactate levels in the blood at maximal exercise appears to be a powerful distinguisher of diseased and nondiseased coronary status.

Characterization of a mucin cDNA clone isolated from HT-29 mucus-secreting cells. The 3' end of MUC5AC?

HT-29 cells resistant to 10(-6) M methotrexate (HT29-MTX) secrete mucins with gastric immunoreactivity (Lesuffleur, T., Barbat, A., Dussaulx, E., and Zweibaum, A. (1990) Cancer Res. 50, 6334-6343). A 3310-base pair mucin cDNA clone (L31) was isolated from an HT29-MTX expression library using a polyclonal serum specific for normal gastric mucosa. It shows a high level of identity (98.6%) to clone NP3a isolated from a nasal polyp cDNA library (Meerzaman, D., Charles, P., Daskal, E., Polymeropoulos, M. H., Martin, B. M., and Rose, M. C. (1994) J. Biol. Chem. 269, 12932-12939). However, as a result of changes in reading frame, the 1042-amino acid deduced peptide contains four regions of a low similarity to the NP3a peptide. The amino acid sequence shows 36.3% similarity to part of the carboxyl-terminal sequence of MUC2 including the so-called D4 domain and 21.3% to the pro von Willebrand factor. A short amino acid sequence is similar to cysteine-rich sequences repeated in tracheobronchial, gastric, and colonic mucin cDNAs. The gene corresponding to L31 is located in the mucin gene cluster on chromosome 11p15.5. The patterns of mRNA expression were indistinguishable from those revealed with the JER58 probe (MUC5AC). Southern blot analysis indicates that the L31 and JER 58 sequences are within 20 kilobase pairs of each other. Together, these results suggest that L31 clone is the 3' end of MUC5AC.

Effects of exposure to hypoxia on the signal-averaged electrocardiogram in healthy subjects

The effects of hypoxia on the signal-averaged ECG (SAECG) were investigated in 26 healthy active subjects with no suggestion of cardiac disease. The SAECG was recorded in each resting subject in normoxic and hypoxic normobaric conditions (inspired O2 fraction 20.7 vs 10.0%) which lowered resting arterial O2 saturation from 98.6 +/- 0.6% to 77.7 +/- 8%. Recordings from four subjects (three men) met the definition of abnormal late potentials at baseline; in all these subjects but one, who exhibited an improved but still abnormal QRS duration, these parameters returned to normal in hypoxic conditions. The duration of the filtered QRS was significantly reduced (from 107.6 +/- 13.2 to 101.6 +/- 11.3 ms, P < 0.01), the duration of the low amplitude signals in the terminal portion of the QRS < 40 microV (LAS) significantly decreased (from 26.5 +/- 9.5 to 22.7 +/- 7.9 ms, P < 0.05) and the root mean square voltage in the last 40 ms (Term-RMS) increased non-significantly (from 55.8 +/- 40.2 to 69.1 +/- 38.3 microV, P = 0.058). Hypoxia determined a higher (P < 0.05) heart rate increase in subjects with abnormal records than in normal subjects. These data could be related to a sympathic discharge. They suggest that: (1) variation in heart rate could affect the SAECG; (2) exposure to hypoxia improves SAECG parameters in healthy subjects, possibly related to sympathetic discharge; (3) abnormal records collected during sinus bradycardia could represent a type of false-positive expression of late potentials in young active adults.

Elevated nocturnal blood pressure assessed by ambulatory automatic monitoring during a stay at high altitude

The aim of this study was to explore, in healthy children, the arterial blood pressure response to a 3-week stay at high altitude (4200 m). An auscultatory automatic ambulatory pressuremeter was used to avoid undue environmental influence on the measurement. The blood pressure was monitored three times in a group of ten boys, aged 10.5 (CI 0.9 years): at sea level (control values), at an altitude of 2100 m after at least 24 h of acclimatization and after at least 24 h at 4200 m altitude. Each period of monitoring extended over 24 h with 10-min intervals between successive measurements. Arterial blood pressure was evaluated separately for the night and day periods. Nocturnal recordings revealed an increase with altitude in systolic as well as in the diastolic blood pressure. Because of the technique used to gather data, this is thought to have represented an independent effect of altitude without interference from the medical environment or diurnal activity.

Decreased mesenteric blood flow in experimental multiple organ failure

Disorders of mucosal blood flow may contribute to gut barrier dysfunction in multiple organ failure (MOF). We evaluated alterations of mesenteric microcirculation in a rat model of MOF. Male Wistar rats received 1 mg/g body weight of zymosan A in 4 ml of mineral oil by intraperitoneal injection and were studied on Days 1, 3, and 5 following injection. A control group received no zymosan. The experimental group also received a fluid resuscitation regimen of 0.9 N saline subcutaneously equal to 0.1 ml/g body weight on the day of zymosan injection and 0.05 ml/g body weight daily thereafter. Day 1 animals tended toward a statistically significantly lower mean arterial pressure versus controls (86.6 +/- 8 mm Hg versus 106 +/- 5 mm Hg, F = 0.09 by ANOVA). Significant arteriolar vasoconstriction occurred on Days 1 and 3 versus control (70 +/- 4 microns and 57 +/- 8 microns versus 96 +/- 3 microns, F = 0.0002). Laser doppler velocity, indicating red blood cell velocity, expressed as a percentage of control paralleled this vasoconstriction (70 +/- 9 and 72 +/- 7%, respectively). We conclude that mesenteric arteriolar vasoconstriction occurs accompanied by decreased red blood velocity. We believe that this is indicative of decreased mesenteric perfusion in this zymosan model of MOF and that survival to Day 5 is associated with a reversal of these microcirculatory changes.

Factors controlling histamine production in Swiss cheese inoculated with Lactobacillus buchneri

Swiss cheese was made from raw milk inoculated with various concentrations of a histamine-producing strain of Lactobacillus buchneri. Histamine production in these cheeses was proportional to the initial number of L. buchneri present in the raw milk. The highest inoculum level tested was 10(5) L. buchneri/ml. This cheese contained 80 mg of histamine/100 g of cheese after 90 d of storage. Only 15 mg of histamine/100 g of cheese were detected after 90 d at the lowest inoculum level, 10(2) L. buchneri/ml. No histamine was detected in any of the Swiss cheese samples until after the brining stage. Perceptible growth of L. buchneri also did not occur until after the warm room treatment. Therefore, control of histamine formation in Swiss cheese requires control of the number of histamine-producing bacteria in the raw milk. A 5.5% NaCl concentration in DeMan, Rogosa, Sharpe (MRS) broth inhibited the production of histamine by L. buchneri, but the concentrations of NaCl typically found in Swiss cheese were not inhibitory. The histamine-producing isolate of L. buchneri survived heating at 49 to 80 degrees C for 10 min, suggesting that this organism would easily survive the normal heating process applied to raw milk used prior to making Swiss cheese.

Persistent arteriolar constriction in microcirculation of the terminal ileum following moderate hemorrhagic hypovolemia and volume restoration

A stable in vivo preparation of moderate hypovolemia with prompt volume restoration was produced in anesthetized rats. The microcirculation of the terminal ileum was observed in vivo videomicroscopy, and changes in mean arterial pressure (MAP) as well as arteriolar diameters were recorded after a 30-min period in which the MAP was reduced by 50% by bleeding. Volume was restored with shed blood alone (control); dextran 70 alone (dextran); or dextran + hypertonic (7.5%) saline (dextran + HS). A final group of rats was pretreated with allopurinol 5 mg/kg and then treated identically to the control group to assess the role of the xanthine oxidase system in microcirculation changes following hemorrhage. MAP was restored to normal by return of shed blood in control animals, but inflow arterioles (A1) remained significantly constricted. MAP was significantly higher and A1 arteriolar dilation was observed in the dextran + HS group. Responses in allopurinol-pretreated animals were not different from the responses seen in control animals. We conclude that persistent arteriolar constriction is produced by moderate hypovolemia and this effect is ameliorated by volume restoration with dextran + HS.

[Value of transcutaneous blood gas monitoring in fiberoptic bronchoscopy in intensive care patients]

Transcutaneous carbon dioxide and oxygen tensions (PtcCO2 and PtcO2) were monitored in seven critically ill patients under mechanical ventilation during fiberoptic bronchoscopy. In these conditions, both PtcO2 and PaO2 and PtcCO2 and PaCO2 correlated, with correlation coefficients of 0.964 and 0.793 respectively. Fiberoptic bronchoscopy induced an average fall in PtcO2 of 42 +/- 2.57 mmHg and an average increase in PtcCO2 of 12.1 +/- 1.89 mmHg; these two parameters returned quickly to their initial values after the procedure. Holter monitoring showed an arrhythmia in five of the seven patients. Continuous measurement of PtcO2 and PtcCO2 was a safe and reliable method for monitoring mechanically ventilated patients undergoing fiberoptic bronchoscopy.