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    83, 84 Blood flow per 1gr of thyroid gland, Blood flow per 1gr of cerebral tissue
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    83, 84 Blood flow per 1gr of thyroid gland, Blood flow per 1gr of cerebral tissue

    Blood flow per gram of thyroid and brain tissue: perfusion intensity, Graves disease and the effects of thyroid hormones.

    Blood flow per gram of tissue shows how intensively an organ is perfused relative to its mass. This application reports it for the thyroid gland and for brain tissue. The brain receives about 0.5 mL per gram per minute, far more than resting muscle. The thyroid has one of the highest blood flows per gram of any organ in classic physiological data, in the range of several millilitres per gram per minute, reflecting its hormone production and release. Thyroid hormones (T4 and T3) in turn regulate the oxygen consumption and metabolic rate of almost all tissues, including the brain.

    ThyroidBrainPerfusion
    Brain≈ 0.5 mL/g/min
    Thyroid (classic data)several mL/g/min
    Resting muscle≈ 0.03 mL/g/min
    Thyroid imagingcolour Doppler ultrasound
    Approximate blood flow per gram of tissue at rest: thyroid several millilitres per gram per minute, kidney about 3, heart about 0.7, brain about 0.5, resting skeletal muscle about 0.03 Blood flow per gram of tissue at rest (approximate) ThyroidKidneyHeartBrainResting muscle ≈ 4–6 mL/g/min*≈ 3≈ 0.7≈ 0.5≈ 0.03 *classic data; Doppler studies report lower values. Others: organ flow ÷ organ mass.
    Figure 1. Approximate resting blood flow per gram of tissue. Thyroid and brain (highlighted) are the two values reported by this application.

    Thyroid blood flow

    Thyroid blood flow is regulated by TSH and the sympathetic nervous system and increases when the gland is stimulated. In Graves disease, stimulating antibodies greatly increase thyroid blood flow; colour Doppler ultrasound shows a diffuse, intense flow pattern ("thyroid inferno"), and a bruit can be heard over the gland. In thyroiditis with destruction of the gland, flow is normal or reduced, which helps to distinguish the causes of hyperthyroidism. In hypothyroidism, thyroid flow tends to be low.

    Brain tissue blood flow

    Brain perfusion per gram is closely matched to its metabolic needs and protected by autoregulation and CO₂ reactivity. Thyroid hormones affect it: in hypothyroidism cerebral blood flow and metabolism are reduced, which contributes to slowed thinking and fatigue; in hyperthyroidism metabolism increases. Low brain perfusion leads to dizziness, fainting and, if severe, ischaemic stroke.

    When to see a doctor

    Palpitations, weight loss, heat intolerance, tremor and an enlarged thyroid, or tiredness, weight gain, cold intolerance and slowed thinking, should be checked with thyroid function tests (TSH, free T4).

    References

    1. Ralls PW, Mayekawa DS, Lee KP, et al. Color-flow Doppler sonography in Graves disease: "thyroid inferno". AJR Am J Roentgenol. 1988;150(4):781–784. doi:10.2214/ajr.150.4.781
    2. Claassen JAHR, Thijssen DHJ, Panerai RB, Faraci FM. Regulation of cerebral blood flow in humans: physiology and clinical implications of autoregulation. Physiol Rev. 2021;101(4):1487–1559. doi:10.1152/physrev.00022.2020

    This article is for general information and does not replace a consultation with a doctor. Measurements must be interpreted by a physician together with symptoms and other tests.

    Published on 1 May 2024