This is usually called hypoperfusion ( Hypoperfusion is a term that describes “a reduced amount of blood flow”. ) and is seen in SPECT scans of the brain. I am experienced with it from episodes of ME/CFS relapse (SPECT scan reports) that had poor memory, poor decision making, easy mental fatigue, increased irritability during the relapse. It is my belief that metabolic changes induced by microbiome dysfunction was the cause of hypoperfusion.
There are some interesting similarities between CFS/ME and ASD, for example:
- CFS/ME has increased Gray Brain Matter and decreased White Brain matter 
- ASD Has increased Gray Brain Matter 
Literature on Autism and hypoperfusion
- Cerebral Perfusion Abnormalities in Children With Autism and Mental Retardation: A Segmental Quantitative SPECT Study  “Generalized hypoperfusion of brain was observed in all 10 cases as compared to controls. Frontal and prefrontal regions revealed maximum hypoperfusion. Subcortical areas also indicated hypoperfusion. We conclude that children with autism have varying levels of perfusion abnormities in brain causing neurophysiologic dysfunction that presents with cognitive and neuropsychological defects.”
- Technetium-99m HMPAO Brain SPECT in Autistic Children and Their Families  ” In parents of AC, significant hypoperfusion was noted in the right parietal and bilateral inferior frontal cortex. In siblings of AC, perfusion in the right frontal cortex, right nucleus caudate and left parietal cortex was significantly decreased. “
- Regional Cerebral Blood Flow in Childhood Autism: A SPET Study With SPM Evaluation  ” abnormal areas are related to the cognitive impairment observed in autistic children, such as language deficits, impairment of cognitive development and object representation, and abnormal perception and responses to sensory stimuli. “
- Effects of route of administration on oxytocin-induced changes in regional cerebral blood flow in humans 
- see Autism and Oxytocin levels, low levels are seen with ASD
- Arterial Spin Labeling Provides a Reliable Neurobiological Marker of Autism Spectrum Disorder  “Arterial spin labeling revealed hypoperfusion in children with ASD in regions critical to social perception and cognition. “
- Altered Resting Perfusion and Functional Connectivity of Default Mode Network in Youth With Autism Spectrum Disorder  “A pattern of altered resting perfusion was found in ASD versus TD children including frontotemporal hyperperfusion and hypoperfusion in the dorsal anterior cingulate cortex. “
- Hyperbaric Oxygen Treatment in Autism Spectrum Disorders  ” A number of individuals with ASD possess certain physiological abnormalities that HBOT might ameliorate, including cerebral hypoperfusion, inflammation, mitochondrial dysfunction and oxidative stress…. A number of individuals with ASD possess certain physiological abnormalities that HBOT might ameliorate, including cerebral hypoperfusion, inflammation, mitochondrial dysfunction and oxidative stress…Studies which used a higher frequency of HBOT sessions (e.g., 10 sessions per week as opposed to 5 sessions per week) generally reported more significant improvements.”
- Brain Perfusion SPECT and EEG Findings in Children With Autism Spectrum Disorders and Medically Intractable Epilepsy  ” In all children, eZIS revealed a mixed hypoperfusion pattern, especially in the prefrontal cortex, medial frontal cortex, anterior cingulate cortex, medial parietal cortex, and/or anterior temporal cortex.”
- Executive Function Deficits and Neural Discordance in Children With Autism Spectrum Disorders  “Children with ASD were impaired in everyday executive functioning and response inhibition. The cordance value, which has been shown to correlate with brain perfusion in a number of studies, was significantly correlated with executive dysfunctions.”
- Brain Perfusion in Autism Varies With Age  “As the age of the autistic individuals increased the hypoperfusion of verbal-associated areas in the left temporal lobe and frontal areas became more evident. The findings were significant at the p < 0.001 level. The changes in perfusion over time correlated with language development and acquisition as individuals matured. “
- The Relationship Between 99mTc-HMPAO Brain SPECT and the Scores of Real Life Rating Scale in Autistic Children  “There was a relationship between bilateral F regions perfusion on 99mTc-HMPAO brain SPECT and the age of autistic children. There was also a negative correlation between IQ levels and the scores of sensory responses, social relationship to people, and sensory-motor responses”
- Perfusion Impairments in Infantile Autism on technetium-99m Ethyl Cysteinate Dimer Brain Single-Photon Emission Tomography: Comparison With Findings on Magnetic Resonance Imaging  ” In conclusion, extensive perfusion impairments involving the cerebellum, thalami and parietal cortex were found in this study. SPECT may be more sensitive in reflecting the pathophysiology of autism than MRI.”
- Personal note: With ME/CFS SPECT was also found to be more sensitive than MRI. My MRI was normal, my SPECT was not.
For ME/CFS, my treatment included sublingual heparin, piracetam and a variety of other items. Below are studies on various items that impacts hypoperfusion.
- Piracetam Ameliorated Oxygen and Glucose Deprivation-Induced Injury in Rat Cortical Neurons via Inhibition of Oxidative Stress, Excitatory Amino Acids Release and P53/Bax 
- Supplementary Management With Pycnogenol® in Patients With Lupus Vasculitis in Remission Phases: A Pilot, Concept Registry Study 
- Intake of Psyllium Seed Husk Reduces White Matter Damage in a Rat Model of Chronic Cerebral Hypoperfusion 
- Resveratrol Reverses the Synaptic Plasticity Deficits in a Chronic Cerebral Hypoperfusion Rat Model  a.k.a. Grape Seed Extract
- Role of Vinpocetine in Cerebrovascular Diseases 
- Effects of Coenzyme Q and Creatine Supplementation on Brain Energy Metabolism in Rats Exposed to Chronic Cerebral Hypoperfusion 
- Eicosapentaenoic Acid: Effect on Brain Prostaglandins, Cerebral Blood Flow and Edema in Ischemic Gerbils  ” Our study indicates that eicosapentaenoic acid prevented post-ischemic cerebral edema and hypoperfusion, without affecting the levels of brain diene prostaglandin and thromboxane.” An Omega-3 acid.
- L-Arginine and Superoxide Dismutase Prevent or Reverse Cerebral Hypoperfusion after Fluid-Percussion Traumatic Brain Injury  only L-arginine was effective
Possible Prescription Drugs
- Alleviation of Brain Hypoperfusion after Preventative Treatment with Lomerizine in an Elderly Migraineur with Aura  (calcium channel blocker)
- [Heparin–piracetam complex and its effect on blood and blood circulation].1998 ““The heparin–piracetam complex had a more pronounced anticoagulant and fibrinolytic activities than the individual components. In addition, this complex accelerated blood flow in the brain.”
Low level coagulation as a contributor to hypoperfusion
For myself with ME/CFS, activation of coagulation was a significant factor and confirmed by labs tests from Hemex (this battery of tests is still available from one lab). Blood flow to the brain can be caused by:
- ‘thick blood'(think of a heavy oil(molasses) versus a light oil (water), one moves much slower than the other). Since blood delivers oxygen, it means less oxygen
- fibrin fibers (‘dirty filters’ that slows the slow, a blood clot would stop the flow)
What do we know from the literature on coagulation and autism?
- Autism, an Extreme Challenge to Integrative Medicine. Part: 1: The Knowledge Base  “Coagulation abnormalities have been reported.”
- Platelet studies in autism spectrum disorder patients and first-degree relatives  “We report increased platelet counts, decreased platelet ATP dense granule secretion, and increased serotonin plasma levels not only in ASD patients but also in their first-degree relatives. This suggests that potential genetic factors associated with platelet counts and granule secretion can be associated with, but are not fully penetrant for ASD.”
- Link Between Autism And Abnormal Blood-vessel Function And Oxidative Stress  “children with autism showed signs of abnormal blood-vessel function and damaging levels of oxidative stress compared to healthy children. The children with autism possessed levels of biochemicals that indicate the presence of constricted blood vessels via the endothelium (the cells that line vessels) with a higher tendency to form clots (through cells called platelets). “
- Evaluation of Platelet Parameters in Children with Autism Spectrum Disorder: Elongated Collagen‐Adenosine Diphosphate and Collagen‐Epinephrine Closure Times 
Most of these issues are replicated in findings with ME/CFS (see links on this page: https://me-pedia.org/wiki/David_Berg).
There are many dimensions here, researched items that I have used include:
In doing this post it was a bit of a surprise to see that 1st degree relatives was seen with similar conditions. For myself, it was not because I have an inherited coagulation defect (Prothrombin G20210A a.k.a. Factor II Mutation) so 1st degree relatives having it is to be expected.
The role of the microbiome and diet for hypoperfusion is not well explore. Emerging Role of Diet and Microbiota Interactions in Neuroinflammation  gives an overview, but implications for hypoperfusion in autism is a to be determined.
This is an EDUCATIONAL POST, the items discussed above (including supplements) should be discussed with your medical professional before starting. This is not medical advice.