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Biomedical subjects

M J Heap

Publications and source records attributed to M J Heap.

6 recordsLinked to original sources
PubMed2006

Slip on 'weak' faults by the rotation of regional stress in the fracture damage zone.

Slip on unfavourably oriented faults with respect to a remotely applied stress is well documented and implies that faults such as the San Andreas fault and low-angle normal faults are weak when compared to laboratory-measured frictional strength. If high pore pressure within fault zones is the cause of such weakness, then stress reorientation within or close to a fault is necessary to allow sufficient fault weakening without the occurrence of hydrofracture. From field observations of a major tectonic fault, and using laboratory experiments and numerical modelling, here we show that stress rotation occurs within the fractured damage zone surrounding faults. In particular, we find that stress rotation is considerable for unfavourably oriented 'weak' faults. In the 'weak' fault case, the damage-induced change in elastic properties provides the necessary stress rotation to allow high pore pressure faulting without inducing hydrofracture.

Journal Article↗
PubMed2000

Acute right-to-left inter-atrial shunt; an important cause of profound hypoxia.

Three patients presented to our intensive care unit over a 3-yr period with profound hypoxia resulting from acute right-to-left inter-atrial shunt (RLIAS). Patient 1 was a 67-yr-old male with an atrial septal defect who became hypoxic and developed the rare sign of platypnoea following elective repair of an abdominal aortic aneurysm (breathlessness made worse when upright and relieved by lying flat). Patient 2 was a 38-yr-old female who developed platypnoea and hypoxia secondary to a patent foramen ovale (PFO) and pericardial effusion. Patient 3 was a 46-yr-old male with a PFO who developed hypoxia without platypnoea because of multiple pulmonary emboli following right hemicolectomy. These case reports illustrate the need to consider RLIAS as a cause of hypoxia of sudden onset. Early use of bubble contrast echocardiography is indicated.

Acute Disease↗
PubMed1997

Are coagulation studies on blood sampled from arterial lines valid?

Coagulation tests were performed on two venous blood samples and two blood samples from arterial lines taken from 79 patients on an intensive care unit. For the first arterial sample the discard volume was 4.5 ml and for the second arterial sample the discard volume was 16 ml. From each pair of venous samples a mean venous coagulation value was calculated. There were statistically significant differences between arterial and venous results and between the two arterial samples for activated partial thromboplastin time and thrombin time assays but not for prothrombin time, reptilase time and fibrinogen assays. However, these differences were sufficiently small to be of little clinical significance. The bias for the difference in activated partial thromboplastin time values between the first arterial sample and the venous sample was +1.24 s (limits of agreement: -4.39 to +6.87 s) and between the second arterial sample and the venous sample the bias was +0.89 s (limits of agreement: -3.25 to +5.03 s). Only 3.8% of first arterial samples and 1.3% of second arterial samples produced activated partial thromboplastin time values that were more than 10% longer than the corresponding venous values. No heparin was detectable in these arterial samples using a heparin assay (< 0.02 iu.ml-1). The differences between arterial and venous activated partial thromboplastin times were slightly but not significantly greater in subgroups of patients with moderately or severely deranged coagulation compared with a group with normal coagulation. We conclude that samples from arterial lines provide valid activated partial thromboplastin time results using a discard volume of either 4.5 ml or 16 ml.

Adult↗
PubMed1993

Elderly patients' preferences concerning life-support treatment.

The preferences of 118 elderly patients, aged from 70 to 97 years, concerning the institution of artificial ventilation in the event of an overwhelming illness, were investigated using a questionnaire. Most patients wanted treatment if the outcome was likely to be good, but in approximately half, the desire for treatment declined as anticipated quality of life or chances of recovery fell. Forty percent wanted to make the decision about institution of artificial ventilation themselves if mentally competent and 24% wanted to use some form of advance directive if mentally incompetent.

Advance Directives↗