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Biomedical subjects

C J Mills

Publications and source records attributed to C J Mills.

17 recordsLinked to original sources
PubMed1992

Measurement of alveolar gas mixing in mechanically ventilated patients.

OBJECTIVE: To evaluate a computer-based, real-time, multibreath nitrogen washout technique in mechanically ventilated patients, incorporating an in-line flow measurement device to measure functional residual capacity and two indices of gas mixing, ventilatory efficiency, and alveolar mixing efficiency. SETTING: ICU, Charing Cross Hospital, London. DESIGN: Within-patient reproducibility of a multibreath nitrogen washout technique. PATIENTS: Seven intubated patients requiring mechanical ventilation. One patient completed two sets of readings. INTERVENTIONS: Patients were connected to a pneumatically driven ventilator fitted with a switching device to be operated either by an appropriate oxygen-nitrogen mixture or equivalently blended oxygen-argon mixture. An inspiratory-expiratory, two-way valve was attached to the delivery port of the ventilator, with a pneumotachograph for flow measurement and a gas sampling probe for gas concentration measurement in line with the patient's endotracheal tube. The analog signals were digitized and handled by a microcomputer. MEASUREMENTS AND MAIN RESULTS: No significant differences were found for any index, with coefficients of variation of 1.5%, 2.9%, and 2.1% for functional residual capacity, ventilatory efficiency, and alveolar mixing efficiency, respectively. CONCLUSIONS: This method gives excellent reproducibility for biological measurements in a clinical setting and shows that these measurements can readily be made on mechanically ventilated patients.

Adult↗
PubMed1991

Correction of pneumotachograph signal for changes in viscosity during nitrogen washout.

Changes in gas viscosity during the nitrogen washout test will affect pneumotachograph measurements. A digital correction technique, using estimates of viscosity derived from measurements of gas concentration, has been described and was examined in this study. The pneumotachograph gain varied directly with argon concentration (coefficient of correlation = 0.995, P less than 0.01) indicating that a simple correction was legitimate. This was tested with an in vitro model, giving very consistent estimates of volume (FRC) despite variations in the ventilation pattern, which were slightly underestimated due to incomplete mixing in the system. Alveolar mixing efficiency (AME) was also reproducible but, like studies in man, fell when low tidal volumes were used. In a repeatability study in six volunteers, examined six times on each of two days, FRC and AME were also reproducible (average coefficient of variation within subjects of 4.97% and 4.34% respectively), considerably better than another reported study using conventional flow measurements. This method appears to be a useful addition to existing techniques for studying nitrogen washout.

Adult↗
PubMed1990

Responses to changes in filling and contractility of indices of human left ventricular mechanical performance.

1. Beat-by-beat indices of contractility for assessment of inotropic effects in a given subject were studied using pacing with beta-adrenergic blockade, in eight patients undergoing routine left heart catheterization. A catheter-tip manometer was sited in the left ventricle and an electromagnetic velocity transducer was mounted further back on the same catheter so that it was sited in the ascending aorta. 2. The maximum rate of rise of left ventricular pressure (dPLV/dtmax), and of aortic velocity (maximum acceleration, MA) and stroke volume (SV) were all obtained with this catheter. Filling effects were assessed by head-up to head-down tilt, inotropic effects by paced post-extrasystolic potentiation. 3. Tilt produced a mean increase in left ventricular end-diastolic pressure (PLVED) of 8.1 mmHg (P less than 0.05), dPLV/dtmax decreased 4.3% (n.s.), peak velocity (PV) increased 23% (P less than 0.05), MA increased 5.4% (n.s.), and SV increased 17.5% (P less than 0.05). Post-extrasystolic potentiation produced a mean decrease in PLVED of 2.8 mmHg (n.s.), dPLV/dtmax increased 35% (P less than 0.05), PV increased 14% (P less than 0.05), MA increased 55% (P less than 0.05), and SV increased 8.7% (n.s.). 4. There was no difference in response between patients with normal and patients with impaired left ventricular ejection fraction. 5. It is concluded that increased left ventricular filling increases stroke volume greatly (Starling effect) but does not affect dPLV/dtmax, which (together with MA) nevertheless responds markedly to increased contractility. dPLV/dtmax appears to be a volume-insensitive index of contractility in the intact human, whether ejection fraction is normal or impaired.

Adrenergic beta-Antagonists↗
PubMed1987

Validation of beat by beat pulsed Doppler measurements of ascending aortic blood velocity in man.

The volume, velocity, and acceleration of ascending aortic blood were measured in man using a pulsed Doppler ultrasound instrument, with online spectral analysis and offline computer processing of velocity data. This system was firstly validated in a test rig capable of generating pulsatile flow of talc particles in water at physiological velocities and accelerations in a model aorta. Doppler measurements correlated well (r greater than or equal to 0.90) with simultaneous electromagnetic measurements of stroke volume, peak ejection velocity, and maximum acceleration in this rig. In vivo validation was performed firstly by comparing simultaneous Doppler and thermodilution cardiac output (Q) measurements; this yielded the following regression equation: Doppler Q = 0.90 X thermodilution Q + 0.03 litre.min-1, r = 0.92; n = 38. Beat by beat measurements were then validated against simultaneous invasive aortic blood velocity measurements made using a Mills electromagnetic cathetertip probe. When paced single beats of different size were compared within subjects the correlation coefficients between Doppler and electromagnetic measurements averaged 0.89 for stroke volume, 0.91 for peak ejection velocity, and 0.79 for maximum acceleration in five subjects. The absolute values for velocity and acceleration from the Doppler system differed significantly from the absolute values given by the electromagnetic system and this difference was not consistent between subjects. It is concluded that the Doppler system can non-invasively record relative changes in left ventricular ejection in man.

Aorta↗
PubMed1979

The absence of protein--sparing effects utilizing crystalline amino acids in stressed patients.

The protein-sparing effects of the peripheral infusion of crystalline amino acids (PAA) was studied metabolically in selected surgical patients subjected to various degrees of stress. Twenty-one patients (sixteen cancer patients receiving chemotherapy and/or radiotherapy, three with major abdominal traumatic injuries and four with paralytic ileus) were infused with 2 1/24 hours of a solution of 4.2% Travasol amino acids with only 5% glucose as a source of nonprotein calories. One-half of the cancer patients were also allowed ad libitum oral intake of a regular hospital diet or Vivonex-HN. The nutritional status was evaluated by measuring changes in body weight, serum albumin levels and nitrogen balance. Body weight decreased in only the trauma patients. When these solutions were the sole source of nutrients all patients were in negative nitrogen balance and had significant decreases in their serum albumin levels. Serum albumin levels were preserved only when extra sources of calories were provided. The infusion of the crystalline amino acids without adequate levels of nonprotein energy did not conserve protein in these stressed patients.

Abdominal Injuries↗
PubMedDate not supplied

The electromagnetic flowmeter.

The electromagnetic flowmeter, which has developed since its inception into a reliable clinical instrument that has become the standard to which all other flowmeters are compared, is described. Perivascular and intravascular transducers now available, which can easily be used to give reliable, high fidelity recordings of blood flow and velocity, are also discussed.

Blood Flow Velocity↗